Here's my background, so you can evaluate the possible biases in what I have to say: I started in split fins, because I was worried about cramping. I dove them for 60 dives, and switched to paddle fins. I have done about 400 dives in paddle fins, and dove my splits for the first time again yesterday. Here's my take.
Split fins give you more power for less muscle effort, if you are doing a standard flutter kick. They somehow manage to give you very little resistance, but still a lot of propulsion. My paddle fins discourage me from doing a standard flutter kick, because they put up a lot of resistance and make it uncomfortable.
On the other hand, splits SUCK for anything other than flutter kicking. I was able to frog kick in them, but it was not pleasant. I could do helicopter turns, but they were inefficient, and I could back kick, but it felt horrible.
If you want to flutter kick into significant current, I think they'd be the way to go. For anything else, get a paddle fin.