I did quite a lot of research when I was looking into what to take up for self defence, and Aikido was never recommended. It looks cool in demonstrations and when steven segal uses it in films, but in real life, against an enraged enemy that will likely not wait for you to grab his wrist without first yanking it out of your hands, it fails. Not saying that you were suggesting it was good for self defence, I'm sure it's great as a sport / demonstrational / recreational art.
When I asked around about self defence, the main responses I got were that it's good to have a decent ranged, close-quarter, and ground game. So eventually, it would be good to do 3 martial arts such as: muay thai (ranged, kicks), boxing (close-quarters), BJJ/Judo (ground).
Krav Maga looks pretty decent, the Israeli army uses it for defence, but it has mixed reviews in those terms. Most (note: most) martial arts can, of course, be used well for self defence, though a lot of them will require many years training before they become mildly useful in real life. Actual self-defence classes with a good instructor, designed to defend against brute force attacks, or a mix of martial arts (MMA/UFC or the ones I mentioned above) is your best bet for self defence.
Fillipino kali and krav maga are what jason bourne took choreography information from, and for that reason alone they're cool (kali being fighting with/against weapons).
Nobody asked for my semi-rant on what constitutes self defence, but there it is nonetheless.
