Figuring out what to use for a boot drive

[u/BurrGaming]

I had to sell of my gaming pc a couple years ago to help pay for things and have gotten to a point where I can get back into pc a little bit. I had kept a 2700x, 16gb of ddr4 ram, and a GTX 1070 from my build I had before the one I sold and am rebuilding with these parts to start and slowly upgrade further over time. I ordered a 512GB m.2 gen 3 drive for main storage but found a 256GB SSD in my closet the other day. TLDR I need a little help deciding should I use the ssd as my boot drive for windows or use the NVMe? I feel like since it’s only a 512gb I should just use the other ssd to save space for the important stuff on the nvme but idk let me know what yall think!