Lots of guys get a car thinking it will help with the ladies but really aren't on the right track. A '70 Mustang Mach 1 will attract lots and lots of 14-year-old-boys who want to hear you rev it and middle-aged men who want to talk about carburetors. 

Something small and cute with no roof like the Miata is a car that most girls might actually be interested in, and be interested in talking about with you. You then have a chance to show her how funny and charming you are ... see where this is going?