I wouldnt do MMA. It's quite violent and in my opinion draws the wrong crowd, because of that. Wushu, being the most elemetary form of (chinese) martial arts, is really interesting, but maybe too 'spiritual' and not practical enough for some. Muay Thai or kickboxing is quite ok, but strongly depends on the teacher you will have. Some will just teach you to hurt people as much as others, whether others will also teach you how to use it responsably and not focuss on the agression alone.
Of all the martial arts i've done, I've liked Aikido the most. It's a beautiful art which combines balance, energy and power into very effective defensive movements. I like it because it doesn't 'breathe' agression, as alot of other forms do. So if you are doing it purely for self defense, I'd say Aikido. However if you also have very high physical demands (you want to work out really hard), maybe you'll be better off doing karate or muay thai. But as I said, the trainer doing the lessons makes all the difference in the world.
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