Both are great cars. I think it depends on what you plan on doing with the car. Is it going to be a daily? The e30 is better for daily use for sure.
For making a fun car, I’d go Miata. You start with dual wishbone suspension, and better weight distribution. Plus there are plenty of tuning opportunities. They weigh so little, that a small turbo makes them a lot of fun.
Also, nothing beats dropping the top on a nice day!