Cant rly say one martial is better than the other. However TKD does kinda have the old problem of it will impress your mum but not your opponent.
A gd TKD instructor can help a MT or MMA fighter with his kicks tho.
When sparring MT i like to occasionaly throw in a spinning back kick that a TKD instructor showed me in the gym.
Shouldnt try and say which is better can draw from the advantages of other arts to improve your area, and in mma should try and draw a little from everything.