Jacare should be higher, Rousey and Shields should be out, and Roger Gracie or Werdum should be in. Hendricks and GSP probably shouldn't be so high either and JJ should definitely be on the list. Dude has subbed Rampage, Machida, and Belfort and rag dolled everyone else. Agree with Maia at #1 though.
Oh, and Warren and Frank Mir are too high, if they should even be on the list. Frank has great subs (really great subs), but the other areas of his grappling aren't that great. His wrestling isn't up to code and his positional BJJ isn't something to write home about.
If I had to pick the 10 best grapplers in MMA (In no order), it'd look like this:
Roger Gracie
Maia
Jacare
Werdum
Jones
Aoki
GSP
Askren
Vinny
Cormier/Cain
Hioki would be on there if not for the fact that he was laid on by Guida and couldn't do much about it.