Tae Kwon Do is great for its kicks and physical fitness.
The only problem is that its pretty easy in the early belts - and if you have the money, the dojo will progress you quite quickly not teaching you the art thoroughly.
Once you get to black belt level, no one can say anything to you because you have earnt it. They dont just hand those out.
Bas Rutten is probably the most famous MMA TKD practioner and he had some lethal kicks - he split a guys liver.