Niether are any good on feather apart from moorhen's in flight but im sure folk will doubt this with a bird that mug's tightly seated game..
Never flown a red tail but i have good info on them..been out with one several times a male never seen him cacth much ..i have had and been out hunting with several harris's and they are good on bunnies but that is about it..unless like is say you are trying to mug tightly squating game bird's..
From my experiences i can not give you a answer on which is best..but i can say both will catch rabbit's.