Well since I've owned a few of those choices, I'll pitch in some advice.
S13 - Ya everyone has them, but it's for a reason. They're very available for pretty cheap, they upgrade nicely, and aftermarket is huge.
AE86 - My favorite car (My current car)!! Tons of fun. A stock GT-S will do whatever you want it to decently (autoX, drift, look good). Aftermarket is decent.
NA(Miata) - Another fun car. I personally thought the convertible was going to be cooler than it actually was. The car shook very bad when going over bumps around town. I upgraded a few things like frame braces, new shocks, chassis welding, but still couldn't 100% get it as solid as a non-convertible. Probably just needed a roll-cage, but I never got around to that. And they're not very practical for everyday use. You basically get a tiny trunk for storage and that's it. They're not for everyone, is basically my point. On a positive note, the knowledge base at
www.miata.net is HUGE. They have so many write ups you'll never have to ask a question about it. (I owned my '90 Miata for a while that's why I have so much info.)
FC3S - Well the one I owned was a PoS, so I don't necessarily know if they're all old and crappy... lol. I had a '89 non turbo. I did all the maintenance upgrades first, and it still ran like crap. Had trouble starting up on cold days. I didn't really how I sat inside of it either, just too laid back. And the blind spots are HORRIBLE since it just has a rear hatch window, no rear quarter windows. Rotary engine was pretty cool, and different. But being that it is so different I felt like a big noob when opening the hood.
I didn't really mean to be too harsh on the Mazda's. They're just not for me. Anyways, hope this helps a little.
- Drifty