Raul is no longer with Blue XT Sea, he has purchased his own boat, he is one of the best DM's I've ever dove with down there. His website is
www.bottomtimedivers.net
B XT Sea has a really good rep, so does Dive with Martin and I have went out with Blue Bubble a lot, which is where I know Raul from.
dive sites depend on the experiance of the divers on the boat and sometimes conditions. but really I can't think of a bad dive spot, they are all a little different, Paradise reef is very shallow, closest to the international pier, but boy! you'll see the fish. the sites further south are deeper and the fish are larger and you'll have some swim-thru's, others are wall dives, really cool! then there's the ship wreck the c-53? I think it's called, just sunk a couple of years ago so it's still under development as far as the reef goes, but it's a nice dive if you've never done a wreck as it's not real deep and it's fairly easy to swim around in.
don't know anything about Hotel Cozumel, usually stay at La Ceiba and like it very much.
so many ops, hotels and sites to choose from, it's a little confusing your first time out, see the sub-forum under Mexico on Cozumel, you'll get more advice there than you can shake a speargun at.
best wishes,
the shark