Id say either the M Roadster or the M Coupe. The M3 is a nice daily driver, but you dont want that if your considering the M Roadster and M Coupe.
You want the M Roadster cause it's a sexy ass convertible car that can still handle track time. You want the M Coupe because it is a track demon and will decimate all. The M3 is kinda more on the M Coupe lines, but not as much, and IMO it's not as eye catching. If you want the ladies, get the roadster, if you want to eat and sleep at the track, get the coupe.