For late December, early January, I'd definitely go Cozumel. Sea of Cortez is going to be cold (Brrrr!), while Cozumel water temps will be about 80 F. - warm enough so that you can do several dives a day with just a 3 mm wetsuit and stay toasty warm. You won't see a lot of big pelagic life in Cozumel, just the occassional Nurse Shark, maybe a few Black Tip Reef Sharks if you are lucky, but you'll see plenty of sea turtles, Morays, green and spotted, barracudas, some larger Groupers, French and Queen Angels, Parrotfish, tons of other fish species, and some amazing coral formations, all in crystal clear water. And I LOVE drift diving. Yes, it does make it more difficult if you are really into macro photography - hovering in one place against a constant current waiting to take a shot of something small can take a lot of effort (and eat up a lot of air), but if you just want to relax, let the current carry you along, and enjoy the view, it's great. And Cozumel is a great place to stay - very safe, very friendly people, and a wealth of very good restaurants. My very favorite dive destination.
BTW, I wouldn't waste any time worrying about the Nortes killing your dive plans. Sure, it might happen, but Nortes are relatively rare, even in the high season, and can happen any time of year. Just depends on wind speed and direction. And, even if one hits, it just might be a perfect day to dive the Wild East Side with Aldora, the only Cozumel Dive Op to dive that side (and usually only when the Leeward side is closed by a Norte - the East Side is usually too rough to dive, but when the wind comes in just right, while the West side of Cozumel is closed to diving, the East side can be calm as a lake - weird). Yes, you might lose a day to diving, but odds are that you won't, and odds are much higher that you won't lose two days in a row. No one can guarantee the weather.