Hi animian,
I won't tell you which fins you should buy, but like a few other people here I have got a number of different pairs of fins that I use for different reasons:
1. Mares Plana Avanti Tres (Closed heel)
I'll use these for long distance pool swims, and warm water snorkelling and scuba. They're quite plyable and very easy on the leg muscles, but still give lots of speed. They don't however have a great deal of acceleration (Not generally required for scuba)
2. Technisub Alas (Closed heel)
Made of a stiff black rubber graphite compound, large surface area and very powerful. Great acceleration, excellent speed. I use these for sprints in the pool, and underwater hockey. Never taken them diving, never will.
3. Cheapo JetFin copy (Open heel)
I've had these fins for over a decade. Been through a few straps, but the fins are still going strong. Lose a bit of power and control through the wetsuit boots, but I never need worry about these guys being bashed around a crowded boat, or being dragged over rocks trying to make an exit in 6" surf..
Summary?
Dunno. I've offered my viewpoints on my personal equipment. I won't offer a subjective opinion on your own gear purchases. Sorry
If you can, definately try a few out before buying.