you just need to work out what YOU want.
the characters of the cars are very differant. ke's and 86s are unique with there short wheel base and ultra light weight, the driving experiance is not comparable.
s12s have obvious potential. but things like RCA's and the like will need to be custom made.
the rear end is also not that great. as far as im aware its trailing arm style and you will get massive geometry changes once you lower the car as much as youre going to want to if you intend to drift it.
because the rear end is nothing like an s13 ect, it is very hard/impossible to correct the geometry at the rear. this is why you see pictures of moddified cars from this era in japan (r31,t/aa63 ect) with MASSIVE amounts of rear camber.
the set up in the live axle version is also inferior to whats under and ae86. there is no panhard bar, the top arms are simply on an angle to stop lateral movement.
the lsd for a h190(live axle diff used in the gazzelle) is basically impossile to get. and extremely expensive.
theyre an extreeeeemely bad prospect come resale time. i have a mate with an extremely neat one who has been struggling to sell it for 2 years. you will lose money.
if youre about to say thats true of any modified car, well to a degree it is, but not always. an ae86 carefully modified you can get out what you put in, and then some. ive done it twice.
an sr conversion will cost the same in a s12, 86 or ke.