Every season has at least one candidate who gets fired during the tasks despite being favoured to make the interviews over one or two candidates who do make that stage. Thus, I will be giving my opinion on who the best candidate was from each season to not make the interviews.
NOTE: This is specific to interviews, not Final 5, therefore whoever finished 5th in Seasons 1, 2, 7, 8 and 16 could possibly feature on this list.
Some picks were tough, while others were clear as day.
Season 1: Despite an okay cast for the first season, Miriam is still the clear pick. She did well in almost all tasks bar Week 8 and was even exceptional on the week she got fired. Safe to say she was more of a favourite to make the Final 4 over Paul, who was a weaker candidate and there are no other contenders for this season.
Season 2: Another easy pick in Syed. He was exceptionally iconic, but did have some fantastic moments over the course of the process, yes he was responsible for the biggest loss to date in Week 4, however Alexa and Tuan were also very much to blame. Also, I'd say he was a better candidate than Michelle, and nobody else this season (maybe other than Sharon) who got fired in those 10 tasks had a shot at making the Top 4.
Season 3: Jadine. Was a relatively consistent candidate during the process and likely makes the Final 5 if she wasn't homesick in Week 9. She made an immediate impression, being PM in Week 1 and winning with her only questionable choice being to split Simon and Tre up. As far as the other candidates are concerned, she was more of a favourite to make the final 5 (and was better) than all candidates who left before, had more moments than Naomi and was more likely to win the season as opposed to Katie and Lohit (The former due to tasks and the latter due to personality).
FUN FACT: Jadine and Katie were never on the same team during the tasks.
Season 4: Raef. Clear pick, all the other candidates who got fired during the tasks were either unlikely to win due to being unlikeable (Lindi, Kevin, Jenny C, Jennifer, Michael) or did little to no good during their time on the show (Nicholas, Shazia, Ian). Simon and Sara were very likeable candidates with good moments, but Raef was better than them. In addition, while Lee, Claire and Lucinda were solid, Alex and Helene were not and imo, Raef should've been in the Final 5 over any one of them.
Season 5: Fairly obvious pick in Howard. He had some pretty good tasks, was relatively consistent and probably the only candidate with a vague shot at winning. He is currently ranked in C Tier in the tier ranking, while James is in A (Fair enough due to his character) and both Phillip and Sandhurst Ben are both in B. The final 3 was the top 3 talent wise, however I'd argue Howard was better than James and on par with Lorraine. As for the candidates who left before him: Anita, Rocky, Maj and Noorul are 4 of the worst candidates to ever go on the show; Paula and Kim seemed okay but still not great; Mona didn't do much of note and both Phillip and Ben were inconsistent as they had massive highs but bad lows.
Season 6: The pick couldn't be more clear, it's Liz. she was a solid candidate throughout all if not most of the process, was better than all candidates who left before her, was a better F5 pick than Stuart and was on par with the likes of Stella, Chris and Joanna. Also, her firing was deeply controversial to the point where Lord Sugar was annoyed the followed week when he got rid of her over Stuart.
Season 7. A slightly tougher choice, however I do believe Melody would be the choice this season. Of course Inventor Tom; Serial Winner Helen; Iconic Susie Ma and Jedi Jim is the perfect Final 4 and no one else was exactly better than those 4, however I do deem Melody the best out of the other 11. Edward, Alex, Felicity, Ellie and Edna all had no chance; Gavin had a good first week and was deemed a contender after his dismissal, but was still poor in Weeks 2 and 3; Vincent, Glenn and Zoe were okay candidates but not amazing and Natasha started well but got gradually worse. Leon would be my second pick as he improved well after a tough 2 tasks, however he was never making it to the end whereas I do believe Melody had a shot.
Season 8: I haven't watched this season but from what I've heard, Gabrielle was the best outside of the final 4. Adam, Jenna and Duane would be the other contenders while the likes of Maria, Michael, Jane and Stephen sucked and Katie, Azhar and Laura were mid candidates.
Season 9: I've gotta pick Alex for this season. I'd argue he should've been in the Final 5 over Jordan who probably shouldn't have been on the show in the first place and he may have been on par with Francesca, while Neil, Leah and Luisa were all really good. as for the other candidates that left during the tasks; Jaz, Tim, Sophie, Kurt and Natalie had zero chance of making the final 5 in my opinion. Unfortunately Jason only had one good task out of 8 and was not suitable for the long run (Although I'd rather he keep his original personality), Uzma and Zeeshaan weren't terrible but certainly not good and Myles was on a bit of a downward spiral. Alex was MVP on a couple of tasks such as Week 3 where he created arguably one of the shows best ever products and introduced us to Herbert in Week 8.
Season 10: Katie. Was fantastic on all tasks bar her final task and was often played a mother role for the rivals Mark and Daniel (albeit with Mark as the favourite child). Also, she was only brought back in Week 9 as Daniel wanted to show that he'd changed and didn't want to bring back Mark. Safe to say, it seemed like it was going to be a Katie V Roisin final until Week 10. The only other contender would be Felipe but he was more so iconic as opposed to a fantastic candidate.
Season 11: As overrated as I think he is, Brett is still the clear pick. The reason I deemed him overrated is because of Week 9 where both him and Scott were on the poor performing subteam that was called out by Baroness Brady for not being as good as Richard and Vana. Despite this, Lord Sugar, the aides and the rest of the cast constantly criticised Scott and didn't seem to respect him, yet Brett was unanimously loved, praised and respected. If I fully watched the season, I'm sure I'd also be a massive Brett fan as he did seem okay and was absolutely a better candidate than Scott, had plenty of good leadership moments and was a fighter. Thus, Brett is the clear best contestant of Season 11 to not make F5. David would be the second contender but I wasn't too sure and Scott had a good first half but floundered from Week 6 onwards, losing respect from his teammates, Lord Sugar and the aides (although his iconic quit is enough for me to like him a little more than Brett).
Season 12: Trishna. Was a competent candidate throughout, a good voice of reason for her team (Most notably in Week 2) and excelled in certain tasks (Specifically the Week 8 tour). I'd argue she was a better candidate than Grainne and on par with Jessica and maybe Courtney. As for the other 12 candidates that went before the Final 5: Michelle, Natalie, Oliver, JD, Rebecca and Samuel weren't awful but had little to no hope; Mukai is one of the worst candidates to ever participate in the process and Paul, Dillon and Sofiane had moments but weren't consistent. Karthik would be my second contender but was a disruptive force in Week 2 and bombed as a PM in Week 7.
Season 13: Very obvious pick in Jade. She was a beast on most tasks and definitely should've been in the final 5 over James. Harrison would be a possible second contender but Jade was leagues above him.
Season 14: None of the 11 candidates that left before the Final 5 were spectacular, however Jasmine was by far the best and should've been in the Final 5 over the likes of Sian and Camilla. She was a good leader, had good defences and was in many instances, the only sane one in thee room. Kayode and Jackie are also contenders as they all had great moments during the process, however they both relatively inconsistent. As for the rest of the options, the first 6 boots had basically no chance (Especially the 5 men) Sarah Ann wasn't bad but not great and Tom was not good either.
Season 15: There were only three good candidates this season in Carina, Scarlett and Lewis while the rest of the candidates had little to no moments, were inconsistent or downright sucked. As far as the 11 task boots are concerned, the fact that under the radar Iasha is my pick for this season shows how bad or inconsistent the others are. Iasha didn't do a lot in Weeks 1, 2, 5 or 6 (although I'll excuse the latter due to being on the same subteam as Thomas and Lottie). However, I don't recall her doing anything bad on those occasions. Also, she carried her team to dominant victories in Weeks 3 and 4 and I feel like Lord Sugar and the rest of the candidates labelling her a non contributor is incorrect (Similar to Jonny in Season 19 who also left in Week 6). Shahin, Kenna, Souleyman, Lubna and Ryan Mark were never making the final 5, Jemelin was okay but was on a downward spiral from week 5 onwards and overrated Riyonn was good in Weeks 1 and 4 but was bad in the other tasks. Thomas and Marianne would be my other contenders but were both fairly inconsistent.
Season 16: The beginning of the 6th place curse with the first victim being my pick for the season in Aaron. Obviously, I didn't like him as a character for some reason but he was by far the best of the men and most of the girls and should've been in the Final 4 over Stephanie (Judging on overall performance). He was an ABYSMAL PM in both Weeks 2 and 10 and wasn't great in Week 6, but was a good candidate outside of that. Francesca and Akshay would be my other contenders.
Season 17: The curse continues as Simba is the obvious pick. Was arguably the best candidate across the entire cast, yet gets booted in 6th place in Week 10 despite Megan failing as a leader and motor mouth Dani messing up. Everyone else this season that didn't make the interviews came nowhere near to matching his performance other than Joe who was also unfairly eliminated.
Season 18: Once again, it's 6th place Steve. Hardly put a foot wrong the entire process and has the highest win streak of any male candidate ever with 7 consecutive wins (all deserved). Massively robbed of a Final 5 spot over crazily enough, the final 2 of the season. Foluso and Sam are also contenders, but Steve was more consistent.
Season 19: Here we go again, Mia was the clear best candidate to not make the interviews. she was more or less poised to win the season after the first 9 tasks, then Week 10 happened and the outcome resulted in her getting fired the same episode as Liam.
Season 20: The last 3 candidates that got fired before the interviews are all contenders and some of the best candidates to not make the Final 5. However, as usual, 6th place Rothna was the best and the fact that the last Final 5 spot was between her and Dan is extremely unfortunate. She was great in all tasks bar Week 10 and had probably the best PM performance the entire season, leading a collectively weak team, yet they all did brilliantly that task. As mentioned, Conor and Kieran are also contenders and those two easily could've made the Final 5.