I have some experience with the SP Twin Jets, Jet Fins and Atomics in a variety of conditions.
Generally I pick the Atomics because they work the best for the kind of diving I'm doing and the kind of effort I am looking to put out.
Factors -
Power: The Twin Jets are the easiest fin to kick in I've used. Almost don't know they are there. It does take some time to get up to speed. The Jet fins are like having my bike in high gear, quick pickup but I get more tired. With the Atomics I get the best mix - I get all the power I need for quick pickup, a decent feeling of resistance and no leg cramps!
Shore diving: The Atomic buckles are amazing. Easy on and off with one hand every time. Very hard to jam with rocks or sand. Jetfins close second, but are a bit more annoying to carry. ScubaPro swivel buckles hold OK but there is no way you are getting them put back together with one hand.
Boat diving: The Atomics are big. On a small boat that can be a hassle.
Generally the feedback on the Atomics is 'just right' for me. I typically use ankle weights, shore dive and have strong legs and think those are all factors.