Power's fine. Needs more curvy roads and a bit more seat time. They're momentum cars, not really power cars. Don't slow down and they're plenty fast.
I've owned all three (Miata, Supra, 240), driven various examples of each. Pros and cons from my experiences:
Supra pros:
-Comfortable
-Good control
-Good winter daily (assuming LSD rear end)
Supra cons:
-Heavy
-Expensive (can be, if you want them to last)
-?
Miata pros:
-Lightweight
-Aftermarket (seriously, check out Flyin Miata sometime for an idea of what you can do)
-Cheap
-Absurdly reliable
-Handling, rain, sun, snow, as long as you have the proper tires, they're awesome
Miata cons:
-Styling. That's about it, at least in terms of daily driving.
-Perhaps mileage. I usually got about 25mpg driving like the throttle was glued to the floor... not great for a 4 cylinder, but a lot of fun.
240 pros:
-Aftermarket
-Styling (they're a good looking car)
-Lightweight, some aspects of their handling.
240 cons:
-"Drift tax"
-Probably not the best starter rwd, but that doesn't apply here
-Finding an S14, or an S13 that isn't beat to shit by now.
-Lightly built cars... stuff breaks pretty easy.
I've daily driven a Supra of one form or another for ~7 years now. If not for a Miata, I can't picture myself driving anything else, and the Miata only comes into the picture because you literally cannot have more fun for less money in a car.
Dude, that's like farting and not telling us what you had for lunch when we accidentally smell it... What did you decide on? It's obviously your decision, and not one of us has any reason to give you a hard time over it.