the rasta keel & the K2 are essentially identical...if you want or like the V2 foil that futures does, get the rastas. if you want a simple, flat foiled fin, get the K2. it's a super wide twin, so you're gonna want more fin area to help generate speed & drive in the conditions you're going to be riding it in & the aipas & T1 aren't going to give you that. there's a reason the fish was developed as a twin keel...drive & speed down the line. the "cut out" on the futures keels will give you a touch more maneuverability w/out sacrificing much in those departments.
the V2 foil is a concave foil on the inside of the fin at the base, transitioning to flat foil as it moves toward the tip. this is intended to help create speed in mushy conditions while still keeping the release that flat foiled fins have. some folks like this, others don't. some can't tell the difference.
honestly, i'd say if you can try them both via finatics, do it. if you can't tell the difference, buy which ever is cheaper.