Go and do one, any one really, it rather depends who is likely to attack you and for what reason, sometimes just fighting back is enough to put them off, no one wants to be beaten up by a girl, other time wacking them on the nose and legging it is a very good choice, if on the other hand you want to be able to completely distroy them then it's a far taller order.
When my youngest sister, who is very girly, turned 18 and was going out and about, I took her weight training to build up her physical conditioning and then to Lau gau kung Fu, 6 months later her physical conditioning was extremely good and she could most certainly break someone's nose or kick then hard enough to make them limp, but the odds of her actually wining a fight against a big determine guy were still quite low, but then she got a big tough boy friend, so it was less important that she could walk round town in safety