We're just finishing up a 5 night trip here and I thought that I'd share some thoughts for anyone considering HM in the area. I know that reading trip reviews always help me decide where to go

Cancun: Eh. I don't think I'd ever really consider Cancun a HM destination unless your plan is to go to a big resort and mostly just stay there. Cancun itself is super touristy and, well, stinky... there is nothing like the smell of sewage to wake you up LOL. Our hotel is at the very end of the hotel zone and I'm glad that we're away from some of the crazy noise/nightlife, crowds, stink. That said, if you live somewhere that doesn't have access to a lot of luxury shopping, that might be cool, and if you like the idea of going to a club once or twice, there are plenty of those and lots of fun nightlife to be had here!
The Westin Cancun: There are two Westins in Cancun, we opted for the one at km 20, at the end of the hotel zone. We pretty much just stayed here because, when we booked it, Alaska Vacations had a crazy good deal and we paid $1350 for air/hotel/taxes/etc for 5 nights for both of us. Can't beat that

So, I didn't do all of my usual TripAdvisor stuff because it was just such a good deal that we figured it couldn't be that bad. And, if you swing a deal like that, it's totally worth it. The grounds here are gorgeous. Two pools, swimming areas in both the lagoon and the ocean, beautiful white sand beaches, multiple restaurants, lots of comfy chairs, etc. I have nothing but good to say about the public/common areas. The rooms are iffy, though. They smell of mildew, stuff is broken, and there is a small amount of mold on lampshades, etc. Also, the only rooms with balconies are the 6th floor (Royal Beach Club, I think). I found out it's only like $35/night more for those rooms and they are nicer/newer, so if you do stay here, go for those! The rooms are large, clean, and nice enough otherwise though. Just not up to Westin standards. However, again, if you catch it on sale, who cares?:)
Playa del Carmen: I think this would really be a great HM destination! It's not too far from the airport (only maybe an hour?), and it's just an adorable little town with a billion cute yummy CHEAP restaurants and little shops. The beaches are also gorgeous. There is even a ferry over to Cozumel. Plus, if you're into the adventure thing, it's close to Xcaret and the ruins at Tulum. Lots to see/do and really cheap delicious food. We spent less today on the best meal we've had, souvenirs, drinks, and gelato than we did at one lunch at the Westin. If you go to PDC, don't go AI! Go to the cute little restaurants!
The only downside of PDC is that the really nice hotels that claim to be in PDC are really a few miles away... so maybe the ideal would be to stay at one of those, rent a car, and explore the town, eat lots of good Mexican food, check out Xcaret and Tulum if that's your thing, etc. I think that's what I'd do if it was my HM.
Anyway, HTH someone