There's 3 dive ops I'd recommend - I've personally used two of them. All the options afaik:
San Carlos, Sonora, Mexico Diving
Most of the better diving is at San Pedro Island about 30-90 mins. away (depends on the boat). There's a sea lion colony there and a deep u/w canyon a short distance off the south end. San Pedro is a vertical, uninhabited rock. On one side, it's sheltered and calm, they do o/w checkouts there. The other side can be a little more challenging. On the ride out/back, you'll almost always see pods of dolphins.
There's also a couple of wrecks in other areas. Vis in February should be good, it's still cold so no algae blooms - expect low-mid 60's.
All of the boats leave from the marina a short drive from town. All the shops are in town so you check-in once then meet at the boat.
The 3 operators I know are:
El Mar Mexico. They have a 36' Newton dive boat. They're one of my local (I live in Phoenix) LDS's and have a sister facility there. We rent tanks from them but I haven't been on the boat yet.
El Mar Diving Center, Your San Carlos Mexico Scuba Diving Center
Gary's is the oldest dive operator there. They have the largest boat - there can be a lot of divers on it. Gary's also has a smaller fast boat and a fleet of older concrete hulled converted tour boats (they're surprisingly stable in rougher conditions) But they're slow. It's a good trip though, once just the 6 of us and two snorkelers - the crew catches fish for tacos while you dive.
Garys Dive Shop - San Carlos, Mexico
Desert Divers in Tucson has an affiliation with Ocean Sports in San Carlos. They run Ocean Spirit, a 46' dive boat with two decks. They'll take up to 36 divers.
http://www.desertdivers.com/store/Ocean_Sports_San_Carlos_Mexico.cfm They have a good reputation locally, my nephew dives from there.
If it's of interest there's a direct flight from Phoenix on USAirways to Guaymas. About a 20min. drive from there to San Carlos - a cab to the marina was $25.
We stayed at the Marina Terra Hotel on one side of the marina. Not beachfront but they have a shuttle to their beach club 1/2 mi. away. You can walk to your boat with full gear - I do.
Hotel Marinaterra - At the San Carlos Desert Bay
Many dive groups also stay at the Best Western Tetakawi in town. It's older but IDK much about it.
Bestwestern.com, the World's Biggest Hotel Family.
There's also several larger condo complexes beachfront:
San Carlos, Sonora, Mexico Apartments & Condos
I've been diving in the Caribbean lately so all this info is about 5 years old. My nephew is doing his DM there this fall thru a Tucson shop so I'm pretty current.
