upper body throws take longer to set up, but they usually put you in a better position than a leg takedown, and they can do more damage to an opponent. i prefer them... but i don't know that they are necessarily faster.
I did my first blue belt tournament yesterday after only having my blue for 1 week. 1st match I pulled guard because I'm not confident in my stand up. My instructor gave me shit. He said it's a poor strategy unless your opponent has vastly superior takedowns. He told me mine were good, so use them. Good advice.
So next match comes and I decide I'm going to get a takedown. Well, that didn't work. Next thing I know, about 5 seconds into the match I'm flying through the air after a judo sacrifice throw. I'm 6-4, it was something spectacular me going for a ride like that, lol.
Turns out this guy cross-trained BJJ and Judo, I should have pulled guard, lol.
Anyway, that's my story on how I was put on the mat VERY quickly.
You took the words out of my mouth txfighter. That or my favorite take down is grabbing collar with both hands and throwing both feet in the hips and try to throw them over your head. If you miss, you still usually get guard.