I'll add my 2 pennies... I have had a '99 and an '01 Miata up until recently... The '99 was my favorite for styling, reliability, etc. If body style doesn't matter, 1994 or 95 cars are best.... Expect to spend about 5,k on a turbo system.
If you want over 200 rwhp, I'd opt for the 94 over the 99. The compression ratio on the 94 is about 8.9:1 whereas the 99 is 9.5 IIRC. The 01+ Miata's have even higher compression, VVT, and are equal in power to the 99. The seats are more comfy, though.
Depends on your power goals, budget, and styling requirements as to which to recommend. I personally wouldn't own an M1 (pre '99 version) because I don't like the looks. I'm an M2 guy, hence my screen name.