cabo san lucas or the riviera maya?

I've never been to either so probably won't be much help, buuuut...we're going to the mayan riviera and I can't wait! Check out El Dorado Seaside Suites

Cabo is probably 'nicer' but the beaches aren't great (since it's on the tip of the Baja peninsula the sea is really rough there). The Riviera Maya is going to have much better beaches in you want to be in the water. In Cabo people mostly stay at their hotel pools. We stated at the Westin in Cabo and it was amazing. The other thing about Cabo is that most of the best hotels are in the 'cooridor' between Cabo San Lucas and San Jose del Cabo. That's great if you just want to stay at your hotel (like if you are doing all-inclusive), but if you want to go into town for dinner, travel to other beaches away from your hotel, etc, the Maya might be a better choice.

You should also consider Puerto Vallarta. I know it sounds all Love Boat cheesey, but we spent a week there last September, and it was the best vacation we've every had. Like Cabo it's on the Pacific, so the water isn't that Caribbean blue like in Maya, but it is in a bay, so the surf it nothing and you can swin on any beach. But the town is just amazing, and there are a millon great restuarants and bar. Other than the first night we didn't eat dinner once in the hotel.

I have never been to the mayan riviera but I was just in Cabo in May and I loved it!

The weather is perfect year round - very little rain since it is basically located in the desert. The sea wasn't rough as the above poster mentioned and if you are into water sports, the Sea of Cortes is just amazing!

I went snorkeling, sailing, rented ATVs, and went parasailing. If you would prefer to stay in the hotel and keep it low-key you can do that as well.

And as a New Yorker, I didn't find it to be very expensive. But obviously, that is subjective.

Good luck in making your decision!