A lot of the dive ops don't even go to the north end of the island unless it's a private charter from what I understand. Too far to motor up there when most divers are staying south of town and the diving south is much more consistant as far as conditions go.
as far as hotels, your going to get as many opinions as there are people here, like Jeff said, the Presidente is very nice and the price is what you would pay for staying at an all-inclusive even though they are not one, but it is one of the nicest resorts on the island.
The best AI I have found is the Occidental Grand, really nice grounds and rooms, excellent food. the draw back is it is WAY south and the cab fare to town is around $17 one way. Thay are also still currently closed due to Emily and I think scheduled to re-open in Nov.??
Middle priced places are the El Cid La Cieba (our favorite) & Hotel Cozumel both very nice properties and the HC offers both AI and non-AI pricing.
At the mid-low end of the price spectrum there is Casa Del Mar and older property but very popular with divers, Caribe Blu also no frills, but clean and very popular here on the board. Fiesta American also falls somewhere in here and I think they have both AI and non-AI packages also.
IF you want relaxing and extra peace and quite, there's the Scuba Club, no phones, no tv, but very nice property and folks that stay there just love it. I think they are in the medium price range.
Your first time to Coz it's really hard to decide on a place, you almost just have to narrow it down to what you want to pay and how close you want to be to town and take the leap of faith. then after your there check out where some of the other
properties are and talk to divers on your boat or folks your run into at restaurants and bars and get their opinion.