> have a good friend who took Judo for 2 years, it looks like a lot of fun, and very effective
I trained Judō for 2 years, more or less, when I was 10~, but because I was pretty anxious all the time I never advanced any belt from white, which is a shame, and now I'm really regretting it.
Yes, indeed, it's pretty fun, useful; and it's not actually that hard; you may want to train your body a bit, though. Trying to bring your opponent down without strength is a bad idea and often ends with your opponent coming in from the defenseless opening.
I'm the Kendō dude from the other thread, and I'd like to learn something involving sword training.
>Apparently a lot of martial arts schools are scams that just teach you flashy stuff instead of actual useful defense techniques (I've heard this about Karate from people who practice other arts.)
I think it depends which place you are training and what you're learning. Some schools/institutions with big names (such as derivated institutions of real japanese Martial Art dōjō) tend to be the place you want to go if you want to learn well, but they also are expensive.
Other place are good while not being "parented" by that kind of institutions.
As for the flashy movements, karate and other "flying" fighting styles tend to be the main target of those people that actually don't teach useful techniques and only "candy-eye" kicks. Other kind of martial arts should not have this problem, but it could happen.