Which martial art/yoga/whatever do you suggest for someone (me--female) who has never done anything like it but would like to achieve just a fraction of the flexibility, fluidity, strength and ability to concentrate that Aud possesses? My age is a factor (58) and weight, too (stocky but strong, but out of shape). Thanks in advance for taking the time to answer a question I suspect you've been asked countless times in various forms.
Until you get fit, the best martial art would be t'ai chi. It can be practiced alone; it has a lovely sense of lightness and flow. Once you are fit, then it depends on what appeals to you. For a sense of sheer power, karate is hard to beat. If you like scrapping about on the floor, then jujitsu might be fun for you. For whippiness, sheer close-in aggression, Wing Chun is pretty good. My favourite martial art is aikido: power, grace, subtlety, precision, fluidity. Wonderful. But it's not for the unfit. If you're not supple, not well knit, you'll dislocate something. So stick to the gentler forms for a while until you get flexible and toned.
In terms of yoga, I like styles that are as much about breathing and meditation and a kind of deliberate attention to the body as they are about exercise. For example, I think Bikram, or hot yoga, is an abomination. It's a bizarre and punishing exercise regime that can be quite dangerous. I prefer styles that fit the form to the body, not the body to the form. People are all different. We're not designed to bend ourselves into pretzels to match pictures in book. So I'd suggest viniyoga, or kripalu. Of the two I like viniyoga best: it has a real sense of flow, and there are lots of floor poses. It's the closest thing to doing tai chi for people like me who no longer balance very well. I hope you enjoy it.