How do you know when a martial art school is legit and not a mcdojo?

I've taken TKD at 2 different schools growing up for 7 years starting at 9 years old. The first very small school (7 people) was ok taught forms, takedowns, punches, kicks, blocks, one-steps, proper technique, some grappling and very little sparring. I didn't like the fact that some of the stuff seemed really stupid sometimes and we did very little sparring so i moved to a different school after 4 years. I went to this other which was a bigger but not a huge school for 3 years, doing the same things except we had sparring once a week and we did things that weren't dumb (although they didn't show proper technique to people as much). I had a 1st degree black belt when i quit and i'm 20 now and wanting to get back into martial arts but more of a style with ground work and I want it to be legit with no goofy stuff. What are things to look for to know it's a good school and what martial art would be good for groundwork?