I initially tried the Mares Razor longfins, but found them too pliant. A stiffer blade suits me better, as I’ll end up churning water with flexible fins. The Cressi 2000 HF is stiff enough without being terribly expensive.
Descending at Airport Beach, Maui.
I’ve been using the same Cressis ever since, and have not had a single reason to dislike them. I sometimes think an even stiffer fin—carbon fibre, for example—would suit me even better. But given the reasonable cost for the 2000 HF, and no discerning reason beyond “maybe it’d be better”, I’ll stick with what I have.
Equalising on descent in our “Blue Dive”, Hawai'i.
I warn you, however—the 2000 HF needs a bit of muscle behind the kick. So if you’re going to surface crawl for a while, you can expect to get pretty winded regardless the speed of travel. I also tend to wear a fin sock at all times to prevent abrasion around the heel: a simple 2 mm sock in warm water up to a 4 mm open cell (the lack of lining makes them thinner in practise) in colder waters.