Re: Self-defense art?
Aikido learning curve is much, I would even exaggerate by saying - tens times longer then many other martial arts, which makes Aikido looking less functional with regards to self-defence. But when you eventually get there you will be capable of some nice things.
I would say is that Aikido is an attempt of refinement of martial arts general concept. I can't judge how far did it get on this way, but what I see is that most people choose it as a martial art that can open "new horizons" in martial and other aspects of self development, rather then the quick way to learn self-defence.
Another think is the purpose. IMHO, Aikido, as it is, has limited capabilities for some specialized applications, such as military attacks or sustained fights, just because it wasn't created and designed for such purposes. And because of that it lacks some necesary for the mentioned applications elements in its general curriculum, as well as some training approaches. And though Aikido can be applied in the above situations, it's usually is not enough to have consistent positive results.
So, the final answer depends on what aspects of self-defence are more or less priority for you.
Just my 0.02.