It depends what you want to do with your fins really.
If you want straight line propulstion then split fins offer some advantages- perceived reduction in cramp, speed through the water, lack of effort required. However they also have disadvantages in that the ability to vary the kick strokes in diminished and pretty much impossible to back kick, with the split effectively working against the diver.
Mares are very good fins and pretty adaptable, giving a good balance of power for the effort put in and reasonable ability to change direction.
I use turtles most of the time as I like the ability to be able to manouver around easily, back kick, and I like their weighting/trim options. The extra stiffness is a help on different kicks and makes tight spaces easier to negotiate. For the type of diving I do I think they offer the best combination of benefits.
If I was reef diving or just wanted to go in a straight line on a very easy dive then I would probably pick Apollo Bio Fins as they were very easy to use, were made out of heavy rubber and offered power for little effort.
Fitted with spring straps of course.
