Ki43 hands down is the best true turn fighter, but as said you really need to take advantage of the elusive nature of the plane as most any hit will finish you. Gunnery isn't as bad as what you would think, I had/have no trouble killing targets with it, you just need to hold a little longer -3 or 4 kill sorties were very normal for most of the dedicated Ki43 pilots, or better.
BNZ, too many to chose from IMO, there are at least 5 that come to mind which are very good at it, K4, F4U4, P51, P47, 190D, and others. Not as easy to determine an outright winner in BNZ IMO.