Cabo is beautiful and the crowd is more grown up than Cancun. Never been to Puerta Vallarta, but have heard great things about it. Congrats on getting married! I am getting married in 1 month as well and we picked Sandals Antigua!
I've stayed in the Mayan Riveria area - near Playa del Carmen. I agree with Chins4 - the vibe there is more mellow. If you haven't checked it out already, look at tripadvisor.com for information about specific resorts. It's been very helpful for me when I've been planning trips. We got married in October as well and we went to Curacao on our honeymoon - it was still hurricane season and we wanted to be outside the hurricane zone. Good luck with the planning - I'm sure you'll have a great time wherever you go!
I love Playa del Carmen Mexico - just got back!
We honeymooned there years ago & keep going back.
It is more laid back than Cancun - I am not into the spring break crowd anymore - I'm 36. I much prefer PDC.
If you're looking for an all inclusive I highly recommend the
Royal Playa Del Carmen. It is fabulous my favorite of all the AIs we've been to - it is also only steps away from downtown Playa del Carmen so you can walk into town for additional nightlife, shopping, cozumel ferry, and dining. It's the best of both worlds.
We LOVE all inclusive but hate feeling isolated. This takes care of that - not isolated at all yet still get the warm fuzzy AI resort feel. This is an adults only resort. You can check it out here: http://www.realresorts.com.mx/The_Royal_Playa_Carmen/