What about kickboxing?I'd say Muay Thai and Boxing. I think boxing and Muay Thai really make for a great combination of skills.
Muay Thai I think is great for self defense because it allows you to strike at all ranges. Even if you never throw a kick in a street sort of situation, knowing clinching, elbows, and knees is great.
Boxing is fantastic because it'll really help you with head movement, footwork and obviously punching.
They're both a lot of fun to learn as well, in my opinion.