Been an instructor for 25 years know so have owned and seen a lot of fins in that time. Heres my 2p's worth
My favourites up until this year have been the US divers jet fins (the predecessors to the Scubapro versions, they were slightly shorter and heavier). they are great for UK cave diving. I have 6 pairs
Also used Mares Avanti's in strong currents. Very powerful, but tiring and very long so hard to use in wrecks
Have recently been converted to Force Fins (Pro) with the bungy strap. Very easy to fin with, powerful, can frog and flutter. Bonus is they are VERY easy to don and doff, and you can walk easily in them. great in the RIB or crowded hard boat. Wont be going back to normal fins ever again. As you may guess I like these a lot
As far as split fins go they are rubbish in UK waters. They may suit nice calm caribbean and Red Sea dives in calm water and minimal kit, but they cant cope with heavy twinsets, drysuits, stage cylinders and stong currents. I see a lot of newbies suckered into buying them (shops profit margin is high) and then binning them for something more suitable. Avoid plastic or quick release buckles like the plague, I see a broken one almost every dive day. The light grey Scubapro ones seem to be the worst of the bunch and produce no thrust at all if there is any kit drag (they do work well with minimal kit). The Mares ones break buckles just by looking at them
But fins are a very subjective issue. Everyones diving conditions and style are different and different fins suit different people. The best advice is to try as many different styles, lengths etc, until you find a pair that suit you. Make sure you add a Force fin to that tryout list though