I had trained in a couple different arts in the past (Tang Soo Do through 1st Dan when I was in HS and college and a few others off and on). When I moved to LA a couple years ago, I wanted to take advantage of the deep martial arts options here (I'm still amazed at what's here). But I stumbled into Alliance Crossfit/KM (then Focus Fitness) with a Google Offer, figuring that having both those things would be great (and it is). I've been there 3.5 years, and while I mostly do CF, I've been doubling my time and adding KM the past year. Agree that it's a great workout, and it's been really eye-opening coming from a traditional martial art. Immediately learned some things that would be big risks in a fight (standing too tall v. head down, punching from hip v. from guard, and sticking punches and kicks v. snapping them).
I was a little primed to learn more practical fighting than traditional martial art. I sparred with some guys in college who just wiped the floor with me due (at least in part) to my limited traditional and point sparring experince (was good at that, but it's SO different from actually fighting). Between that experience and some failed demos for friends where someone with grappling/wrestling experience quickly took me down, I was ready to learn techniques that work.
I also like the "keep it if it works" philisophy, and I stay with Alliance because of the atmosphere and training (high intensity, but no thugs, and not too "jocky" or MMA focused, although they have a "fight class" I'm itching to try).
Not sure if this is the same at other schools, but they have a very informal but serious approach to training. No gi or belts, just a Krav tshirt (and they aren't too strict about that). They say "don't call us sir or ma'am". It's funny that despite the military history, they're much less "martial" than traditional arts (few static "in-line" exercises, no tennets to chant at the end of class). I like all this, and I like that it's serious and focused, without being "disciplined" in the traditional (and shallow) sense of the term.