What martial art would be more effective in a violent altercation Mauy Thai or...

Either one.

Depends on what the other person does, and what your natural reaction is.

Against someone with no martial arts (considering street fighting a style here as I know street fighters who are the equal to any black belt) either style will do well. They're both sports, but against someone without training they're vicious.

As to which one will be more effective, that depends on the martial artist. For me, with my long legs and long arms, I'd be better off with Muay Thai. On top of that I'm not comfortable grappling. Too much of my training has been focused on NOT ending up on the ground. For a smaller person with different training, BJJ would be better.

Brazilian Jiu Jitsu, grappling is something you have to learn and know the technique to be effective and once you take them to the ground they won't know what to do. If you keep it standing with Muay thai everyone has a punchers chance.

Muay Thai. I don't have much experience in it, but I know that traditional muaythai from Thailand is pretty brutal. For BJJ, it's not to useful in a streetfight when there can be glass and sharp objects and such on the ground. I say that muay thai would be more effective in a street fight.

both of them. you should learn how to fight on the ground as same as you learn on feet.

because fights usualy end up on the ground.

You already asked this question..

if the other person has ZERO ma experience I say BJJ, subbing a newbie is supper easy, regardless of who they are.

Some guys can still punch pretty damn hard wo training

Gonna tell you something firsthand, you do NOT wanna be on your back in a "violent altercation". Layin there like your boys on television will get your head kicked in that much I guarantee you. Them guys got rules, although many of you think that what you are seeing is a "real" fight, it's very far from it. Why? They're not expecting the other competitor to bite the sh*t out of them or to kick their head around the floor. And while you may think that weapons never come into play, you are largely mistaken.

Muay Thai is one of many martial arts no one ever f*ckin heard about till it hit Spike. Kick a determined motherf*cker in his leg and see where that gets you. Knee him in his face in your little clinch position and hope you pull it off before he sucks that leg in and beats you lifeless.

Keep at it though, you're gonna find out one day that what you watch on TV ain't how it plays out in real life. Unfortunately for you, you'll learn this on one sad occasion when all your training betrays you.