Going off some old experience, since I haven't played lately.
The 190s are all over-rated, at least on the boards. They'd rate somewhere between the B-24 and the A-20 as a fighter.
The Spit 14 is over-rated by the perk system, a 109K is just as good.
I actually think the Niki is over-rated. I personally can't stand it, it took a large whack with the nerf stick during the transition from AH1 to AH2.. and it has never been the same. In AH1 it was a bona-fide killer - I'd have taken it over any Spit/turny plane. AH2 it is meat for any Spit but the 14, the Hurri2c, and the Ki-84 (which is under-rated, imo.. although compared to a Spixteen no wonder nobody flies it.. or anything else).
The P-51 is over-rated, in my opinion. Unless they un-nerfed it since I stopped playing. Before it inherited the turning radius of a dump truck (or 190, take your pick), it was a good all-round fighter.
Thats all I can think of. Just my 2c.