Despite being Hollis, the F1 (super heavy batfins) and F2 (very lightweight and maneuverable) are pretty nice selections - the F1 for cold water with good negative buoyancy and a bit better fit than a lot of the jetfin/turtle clones for me. The F2 has a different fit than the F1 but they're pretty maneuverable and super lightweight. If you put some lexan / tarp / plastic over the holes on the bottom you get a lot more thrust as well.