I started out with JetFins and never used anything else until last year, when I got some Atomic split fins (and kept the JetFins, of course).
I never really understood the occasional complaint that the JetFins were "too hard" to use, or caused cramping, etc. I always figured that, if you used something that made your muscles work hard, your muscles adjusted to it. I don't think there's any better recommendation for the JetFin than the fact that they have been around for so long and so many experienced divers keep using them. People can still have their own preferences, but if you *don't* have a strong preference for something else, it's hard to go wrong by choosing what an awful lot of the more experienced people around you are using. I feel the same way about buying anything, and I rarely feel that I have wasted my money that way.
In any case, over the years most of the discussion I have heard about JetFins and other fins with similar design (Turtles, etc.) concerned the size of the foot pocket. A well-designed fin that doesn't fit well isn't going to be as efficient as a slightly "inferior" fin that fits properly. I could only recommend the "original" ScubaPro JetFin for this kind of fin, because it's really all I have ever known. But if you couldn't find one that fit properly, or get it to fit properly with a different boot, I wouldn't hesitate to suggest going with an "imitator" that fits better.