Second the Scot ...
For roomy daysailing (no cabin), with four+ in the cockpit, and yet still fitting in the garage, the Flying Scot and similarly sized Rhodes 19 are great choices. Proven designs, plenty of solid used boats out there.
My Scot on the trailer fits diagonally in my conventional two-car garage (currently a boat renovation shop), and the mast also fits, pulleyed up against the ceiling. It's got a huge cockpit (as does the Rhodes). I can pull it with my V6 Accord (although I won't take it terribly far), it launches easily, it can be singlehanded well. Set up is simple, but it can certainly be tuned for performance.
The Daysailor is a somewhat smaller choice, but probably perfectly suitable, too.