We will be going to Cancun in December. Any recommendations on which set of ruins to see? how close each is to Cancun? any info or recommendations are appreciated!

The two sites aren't really comparable/ CI is a sprawling Maya/Toltec city with outsize monuments, temples and ball courts. Tulum is a small late Maya city. The architecture is crude, but the setting by the sea is beautiful. Tulum is at least an hour closer. See both if you have the time. You might also add Coba, which is past Tulum and inland.

You could do both but in the same day? I'm thinking not. CI is a long full day by itself. For Tulum, do the ruins early and spend the rest of the day on the beaches south of there. They are the most amazing beaches in the world!!

Who said anything about the same day?

Just clarifying......

If you have time and are up for it do both, and even Coba if possible. You must allow a whole day for CI as you will probably do it with a tour (we used Gray Lines and they did great job, included bus transport on A/C bus, lunch at the nice hotel next to CI, free time at the ruins, then back to Cancun). Tulum will not use a whole day but it is not real close to Cancun either since it is south of Playa Del Carmen. Again, if you do not want to rent a car use a tour. Car rental is an option and it would be possible to do Coba and Tulum in same day but doubt if any beach time would be available. The drive to Tulum is easy from Cancun, and the drive to Coba from Tulum is pretty good as well except for the last few kilometers and even those are not bad.

Of the three, CI is the best excavated/restored, Tulum is set seaside overlooking a beautiful beach, and Coba feels like it is deep in the jungle and is pretty rustic. We liked all three. Oh and at Coba, unless things have changed in the last year, you can still climb the ruins. Not so at CI or Tulum.

Have fun!

We rented a car at the airport, spent a day resting on the beach at Cancun. Drove to CI on the autopiste.
Well sign posted, and the trip took 2 hours,very little traffic. Plan on spending the entire day there.
Next day we drove to Coba in the AM and did Tulum in the PM. Both are easily doable in a day. Road to Tulum is good, to Coba there are a few rough spots. Good suggestions about the beaches.
If you have time take the boat to Isla Mujeres.

We just returned from 10 days in the Yucatan last week. You could see both sites in one day. A couple of hours at each site is more than enough. I’m not sure how someone could spend an entire day at CI…even the guided tour is only 1.5 hours.
We saw 5 ruins: Tulum, Chichen Itza, Ek Balam, Uxmal and Kabah. Chichen Itza was at the bottom of the list and Uxmal was at the top. Ek Balam was fantastic (my second fav) and only 30 minutes from Chichen Itza.

I would suggest renting a car for the day to give you more flexibility. Get up very early and take the Cancun-Merida toll road to Chichen Itza which will take around 1 hour from Cancun. If you get there when it opens at 8am, there are not any crowds and it is still cool. Then head over to Ek Balam around 10am and then cool off in a Cenote around noon. Grab lunch in Valladolid before heading to Tulum in the afternoon and bring your bathing suit to swim on the beach at the ruins. Follow signs to Tulum on road 180. There are lots of road signs.
Or if you don't want to rent a car, there's plenty of organized group tours on an air conditioned bus that do the same route…just more crowds and less time.

WOW one hour from Cancun to CI! That is some fast driving. Good thing the local cops were not issuing tickets or you would have learned the true cost of that speed!

Perhaps I should have specified that it depends on the driver....anywhere from 1-2 hours to CI, depending on your speed. It took us 3 hours from Centro Merida to Playa Del Carmen...hubby was driving over the speed limit to make the ferry over to Cozumel. We must have seen only a total of 10 cars/buses on a Sunday afternoon. Not many want to pay $33 US for the trip. Plenty of cops at the toll booths with machine guns. At every road block during the trip, they waved us along because we were tourist...same at the tolls.

We probably won't rent a car as there are 12 of us; we will have 7 adults, 3 teenagers, and 2 little ones aged 4 and 6. The information given here has been great~I'll forward all of the info to the others and see who is interested in what.........we may end up seeing different things!