muay thai, BJJ, or (possibly) both?

To be good at a martial art, you have to train several days per week for many years. That said, I would suggest you try some trial classes of both and figure out which art you like from there. Once you start, get serious and devote a few years to training. Obtain at least your first dan (black belt), then decide if you want to move to the next.

Things to consider:

1. what do you want to get out of this?

2. do you prefer striking or grappling?

3. which teacher do you respect the most?

BJJ or Judo,striking is not necessary. BJJ is a complete art,if strong strikers could beat grapplers than Royce would not of won the UFC..multiple times. Fighting at least 4 fights a night..,and winning all of them.. also There is this video on youtube,this Purple belt was at a gas station and some shirtless guy was acting violent,and rushed at the man,and the guy went for a shoot,and put him in a rear naked choke,without throwing 1 punch,it was over and done in 5 seconds. He didn't get hit either

I'm not really sure what BJJ is but i say go for muay thai is cool and you can use the moves you learn in real life situations. I'm not sure how old you are but 5-4 is kinda small (not to be disrespectful, im short too) having martial arts skills could help to build up your confidance and self-esteem.

Muay Thai is a pretty devastating fighting art - BJJ is great for ground work and submissions

If I was you I would try some classes in both and see what you prefer

If your goal is to be a well-rounded martial artist, than taking both makes good sense. Muay Thai is an excellent striking art; one that makes use of fists, elbows, knees, shins and feet: It's dynamic and will get you in excellent shape. Brazlian Jiu-Jitsu is an excellent grappling art; one that makes use of chokes, armlocks, leglocks and teaches one how to control an opponent should the fight go to the ground, which often happens. It will also improve your fitness and stamina.

Individually, they are both effective forms of fitness and self-defense: Combined, they will make you a well-rounded martial artist; providing you with an enviable arsenal.

Take both. Muay thai is all striking, BJJ is all ground fighting, and submissions. Take both and get the best of both worlds.

taking either of them will be incomplete. taking both of them will be much more complete. if possible i'd take them both, at least long enough to figure out which one i like best.

they are both good at different things