I think the question, or at least the answers, are far too broad.

First of all, are we talking 90's still?
And body lines don't change within a generation. The '88-92 MX-6 is the same for every year, every trim. Unless you count the black trim around the doors on the GT's, or the different grill on the later models. But is that enough to say it looks different? Not to me.

The 1st gen RX-7 had 2 different engines, and several trim levels. But they all look the same. So are we talking performance, or looks?

For rotaries I'd go with the 1st gen, because that was the first major production rotary in the U.S., and in a car with (to me) timeless beauty. The 3rd gen holds value perhaps, but it never was cheap. Twin turbos complicated the engine for the do-it-yourselfer.

I guess I am really just biased towards Mazda. Looking out my window I see the resemblance to the early Z cars, but looking under the hood I know I have something completely different than any other auto manufacturer dares to produce.