Angela we had the same issue as you in the beginning. We initially chose the Riu because it was SO much cheaper for our guests (like $600 cheaper per person...$1200 per couple. That's a LOT if you ask me!). But then we had some issues with our travel plans last month and re-priced things and Dreams came out at the same price we had before for the Riu, so we switched. In my opinion, Dreams weddings are nicer. Riu is a great, fun resort though! Your guests will love either...I would pay more attention to where you want your wedding to be. I think Dreams is much more open about bringing in outside vendors as well. I'm not using any package at Dreams...I'm bringing in everything on my own (flowers, cupcakes, furniture rental, hair stylist). I think the Riu wouldn't have let me do that. So it's totally dependent on what you want your wedding to look like really!
Good luck - you really can't go wrong with either choice. Cabo is amazing.