The S2000 has a fantastic engine and handling. My friend S/C'd his to 390whp for a little over 11k, so it has tons of potential. It's also great stock and I'm sure it's a blast to take to the track.
In my opinion, the Miata became obsolete the minute the first S2000 rolled out of the factory. The only thing the Miata has to it's advantage is price.