Anything is better than nothing, if there's a simple Karate joint nearby, why not?
Hapkido is a sort of unique martial art, it's hard to explain but overall it can be summed up nicely by the phrase "Be like water". In Hapkido if an attacker is coming at you to punch, you would grab his arm then roll or dive backwards, doubling the momentum, then twisting, releasing, and sending him on a nice sprained/fractured arm air vacation (aka the type of air tvacation where you can't catch yourself to soften the blow, you'd just land on your head/neck). Hapkido's main thing is to use someone's momentum against them to inflict damage, and thus, most of the moves and techniques are based around that philosphy of fighting. Unlike kickboxing and Brazillian Jitsu, they will teach you how to kill people. I had a lot of fun when I took classes, and I can't recomend it enough.
Then again, there is no "best" martial art/sport, and there's certainly no guarantees in any of it. But that's what guns are for
If you're not too serious about unarmed fighting, but want to know a few tricks, just buy a book off of amazon. "Kill or Get Killed" and/or "Get Tough" are more than enough to back up anyone's CQC abilities.