Do both. A lot of schools these days will offer both. If you're thinking self-defense, Muay Thai has a lot to offer (ranged striking, clinch fighting), but if you end up on the ground, you need to know some escapes, an if you want to end a fight without doing your opponent serious damage (a drunk relative/friend or something), you need to know chokes or pins; BJJ has those, while Muay Thai doesn't.

You know I'm getting real sick and tired about people asking about "the best martial arts". You must be the 10th or so person today to ask for the best martial arts. Just go for muay thai. It seems to be what you want so go crazy.

ya know theres really no best martial arts.. they all have strong points and weaknesses.. its best to learn both to be honest... muey thai is a art that teaches how to standup and fight with punches,knees, kicks, elbows ect

brazialin teaches mostly fighting on the ground... taking your opponiant down and fighting on the ground that includes chokes breaking arms legs knees ect...

do both

Which is the best? I'd like to defend myself in a street fight and I doubt there is gonna be much grappling going on in a street fight so I think I wanna do muay thai, but most of the pros in professional mma have BJJ has their art, so I'm really wondering which is the best.