Kuchikis bankai is pretty well delivered imo. Hitsygayas is overall the best in terms of having both awesome defense and offense, and can regenrate itself, so I like his as well. Actually most bankais are awesome just Ichigo, Renji, Soifon's are really lame.
Read the manga then act, problem solved!
Actually no scratch that, it's been drawn out there as well. lols