+1 to bouldering bum's general sentiment
A few years ago I decided to pick up a martial art. I was initially really attracted to the idea of wing chun. Seemed cool. Decided to do some foot work and see if it was legit. The short version? Any martial art that does not have as it's focus (or at least a major focus) competition under relatively open rules is a joke from the martial
perspective. Aikido, kung-fu, most karate, etc. are not going to help you defend yourself. The reasons are a few. Including both (A) the fact that you can't figure out good practice from armchair fighting--it involves an incredibly large number of variables, and if you don't compete against someone who's actively trying make you lose there's no way to separate wheat from chaff (B) even if you're learning good technique, you won't be able to apply it unless you actually spend the many, many hours doing competitive training to learn how to translate the techniques to a live environment (timing, weight application, counters, etc.).
There are lots of different kind of aikido, some more philosophical in bent some less so. But, having done both judo and brazilian jiu jitsu (two competitive sports) with aikido black belts it does not translate well to practical applications even in good cases. Which is not to say it's useless, but... it's mostly supplemental. And in some cases it's just a joke practiced without context. For example, there's a lot of focus on hand grabbing and wristlocks from a handshake-like position. Usually trained as though such movements have some general applicability when they're actually inheritance form a time when a samurai wanted to stop another samurai from drawing a sword. It's like a game of telephone, the meaning get's lost when repeated over and over again without any objective standards to judge technique against (competition).
That said, the applicability of any
martial art in a self-defense situation is worth questioning. If you want to get really good it takes a lot of time. If you're playing the odds, you'll spend a lot more time training than you would likely have lost do to getting hurt by some thug unless your circumstances are particularly dangerous (e.g. cop). I train because I love the sports. Applicability in a self-defense situation is a bonus, but, is also limited. A lot of common self-defense situations that world class fighters probably wouldn't be able to get themselves out of. (If there are more of them than you, or they're better armed, things are definitely not looking so great. ;)
Short version, if you are concerened with actual applicability to a fight take up a martial sport
. For a decently sized guy boxing or the like (e.g. muay thai, sanda) will give you the best bang for your time invested.
Ground based fighting like BJJ is really powerful in one-on-one situations, especially if the other guy is significantly stronger. That said, if you're in (for example) a bar, or any case where there's a good chance that the guy has a buddy nearby you probably don't want to go to the ground. My opinion.
(Oh, one other thing. Some people like to say "it's the martial artist, not the art" - that's BS. If that were really true you could just make up your own damn martial art. Not all martial arts are created equal (and even within them, not all gyms are created equal). The early UFC's and vale tudo fights in brazil that pitted styles against eachother made that inequality very clear. In case this comes up. ;)
pps: (sorry this is so long
Wherever you go, please, please, please be sure to do your homework. There are bad instructors and outright frauds out there. Lots of good online resources to look into these things. If you're interested in anything MMA ish (bjj, muay thai, boxing, etc.) look up some mma training forums and ask people's opinions before committing to a gym. Good chance you'll be glad you did.