Since you're traveling solo (which, btw, I did to Fiji a couple of years ago on a budget 11-day dive trip, and it was great--you could manage those 9 days easy), I'm thinking some hotels are more conducive to meeting people than others. Since most people who stay at both Blue Angel and Villa Aldora dive with the respective associated dive shops, there should be a fair amount of congregating and chatting. I know there is at BA. Villa Aldora has a nice-looking beach area, but we haven't stayed there. We've been diving with both, and we like both very much, but for different reasons. Since you're planning on having a car, there is one hotel, Ventanas al Mar, on the scenic, sandier east side of the island. You'd have to drive to meet your dive op, though. Otherwise, most of the beachier places to stay are big resorts to the south and perhaps smaller resorts to the north. As discussed, south makes for convenient dive access, north less so, with perhaps the exception of Aldora.
Not sure what you mean by "crowding" dives. Most of the popular dive shops that get discussed here send people out in small groups, and those with more than one boat do tend to group people by experience levels when they can. But many do use small boats, and in that way, one could consider the boat crowded.
We've stayed in town a few times, and although you do end up giving up easy access to beach swimming and shore diving (not Cozumel's strength, but still nice to do), you gain the livelier pleasures of town, people-watching and convenience to local restaurants. If you stay in town, you have to give a little more thought as to how you're going to meet up with your dive shop (not all pick up downtown), but again, if you have a car, that eases your options--but not necessarily while meeting your desire to be a few steps from your dive pier.
We really like diving with our favorite DM at BA, and there's one other there we like who is a phenomenal critter spotter. We really liked one of our two DMs at Aldora, and they're generally top-notch all the way around. Our experiences with almost all the ops we've tried over the years have been good too. Under the right circumstances, we'd also try Tres Pelicanos--we talked to them a bit this trip, and they have a pretty sweet boat.
