In the Mazda MX5 Community, there tends to be massive debate over this issue.
Im currently runing Toyo Proxes T1R's although I want to try some Goodyear Eagle F1's at some point but these Toyos don't want to wear out, but I'm really happy with them.
I know the T1S's wear quickly but I've heard loads of good things.
I tend to run my Toyos higher than stock psi as they have softer sidewalls.
Stock psi is 26psi but I run 29psi, I find this helps the cars handling.
Tony has already worked his magic on my car, in fact not long till I go back.
Other good brands from the 5, include the already mentioned Potenza, Yokohama Advan Neova, Kumho Ecsta and Falken Azensis.