I'd definitely recommend going with a group and heading by bus. I probably wouldn't drive myself. Tulum and Chichen Itza are FAR. 2-3 hours away. It looks close on a map, but it's a haul. Be prepared to dedicate most, if not an entire day to each. I love Cancun because it's easy to get around. For a few pesos you can hop on and off the bus that goes along the main strip. If you're looking for a quieter town I'd recommend Playa del Carmen. It's just South of Cancun and much less of a party place. Lots of big resorts and condos, etc.. If you stay in Cancun I highly recommend taking a boat to Isla Mujeres. Rent a golf cart and go explore the island. It's a blast. Either way, the area is beautiful and you can't go wrong with anything you decide to do.