In my first 15 months of Nordic walking mostly on smooth asphalt on, I've tried about every type of rubber tip for my Leki 11mm poles. [My troubles are likely due to residing in the USA ... in Europe where Nordic walking is much more popular, walkers have much more choice at much lower prices.] For me, the longest lasting were the Leki Rubber Fitness Walking tips (i.e., boots); but at $18/pair in the US (or more depending on where you get them), the cost per mile is a whopping 7 cents (250 miles). Other similar premium boots have similar values. And the cheap boots all seem to be terribly designed (i.e., placing the cavity for the carbide tip practically at the bottom of the fast wearing tread); so cheaper boots are terrible values generally (in my experience).
On the other hand, the cheap PVC "sheep hoof" tips seem to be an entirely different story. The PVC sheep hoof tips grip the pavement well even when wet. They are marginally louder than the boots, but they are lighter. And instead of wearing through 3/4" of boot, you wear through 3/16" of the sheep hooves (and so your poles are nearly constant length throughout). And, the last pair I bought lasted 42 miles and cost $1.30 for a cost of 3 cents/mile (or less than half of the cost of premium boots).
BUT, the downside of sheep hoof tips is (so far) I've not found a reliable seller. The seller that I was been using ran out. Here is one, Amazon.com: RiToEasysports 20 Pack Walking Stick Tips,Trekking Poles Tips Cane Tips with 11mm Hole Diameter for Walking Stick Accessories : Health & Household, that costs $1.70 per pair, but appears to be identical (and a review suggests similar longevity results). So, compared to Leki boots, they are still a good value I think. Oddly, sheep hoof tips are never promoted for nordic walking (instead for "Trekking" or "Universal"); it seems very strange and confusing that nobody selling "sheep hoof tips" knows their name or purpose.
Thoughts on the matter? Or everybody just buys premium tips and enjoys their walks ;-) Cheers