What martial art is most suited for a street fight?

The simple answer here is that all of them are. If you think karate doesn't work, you've never fought a real karateka. If you think muay thai doesn't work, then go pick a bone with the thai special forces. The fact is that every art will work in a street fight. Why? Because that's what they were made for! Listen, the most important thing is the instructor. While any art will do, if the art is taught poorly it won't help at all. Making sure the instructors are good is the most important part.