An age old question!
Okay, here's my take on fins, split vs. paddle.
First of all, it is a good idea to more accurately define the type of paddle fins. Some are relatively soft and others are much stiffer. So when asking about paddles (or blades) vs. splits, it is a good idea to be specific about the kind of paddles you are talking about, stiff or not so stiff.
I've used various types of paddle or blade fins, including jets (both xl and medium) Diverite blades (two sizes), OMS Splitstreams, Aqualung Slingshots as well as various cheaper rental fins. I have also used Scubapro split jets.
I find with the split jets, I can easily over kick them. When I need real power, such as trying to get back on a boat, or finning fast in a current, the splits just don't seem to give me what I need. Oddly, I also get cramps when I wear them --which doesn't seem to happen with most paddle fins.
The softer paddle fins feel much more like splits, and don't really have the force I need in current, which is why for technical diving I rely on paddle fins, like the OMS Slipstreams.
For general diving, I use the Diverite fins and for purely recreational diving I really like the Aqualung Slingshots.
If I am diving doubles, a rebreather or pushing a big camera through the water, I rely on the stiffer paddles. I also use paddles if I know there will be current.
I have sold my Split Jets.
Jeff