Well honestly speaking both of them are great skills.
Comparing both in a realistic fight point of view, I would say Muay Thai is slightly better option cause it's simply better rounded. You have an option to be a more diverse fighter in Muay Thai, which is probably why you are provided with more classes as well. Not to take anything away from boxing though, a good boxer could easily take out an average Muay Thai fighter and vice versa.
Interested in training at home to become a BEAST MMA fighter? Click here.