I need to join a self defence class in New Zealand tha very interesting and enjoyable and cheap too. I used to be doing gym stuff that about 15-20yras ago now I am 40yrs old, 5′10” tall and 126kg.
Aikido i think is the best for only defence
it teaches only for self defence,, not for fighting
there are so many movements which are just for weakening our opposite,, it hurts cause its positions make our opposite will get hurt more if they move
hope that helps 
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jiu-jitsu. its mostly grappling and is great for defensive manuevers.
also its good to look around. take a calss here, one there, and see what you like.
if your looking for a workout i would recomend some sort of kickboxing.
References :
Aikido i think is the best for only defence
it teaches only for self defence,, not for fighting
there are so many movements which are just for weakening our opposite,, it hurts cause its positions make our opposite will get hurt more if they move
hope that helps
http://tipsandtricks-vista.blogspot.com/
earn money by searching Yahoo
http://www.myhpf.co.uk/apply001.asp?Friend=113587
References :
Thai boxing a.k.a. Muay Thai, you will be burn lots of fat.
There is Kick boxing aswell but that is if you are trying to build muscles.
References :