We have done both and they are both very long days. Chiz was better then tulum in my opinion. We heard there is a night show at chiz that is really good. Might be an option for ya too
We found another one close to the hotel zone also which look pretty nice it's called El Meco Ruins which we're going to visit this trip.
I've been to Chichen Itza before and loved it but didn't really love the bus ride. This will be my husband's first time going so I wondered about taking him there or Tulum so I'm glad you posted this. Here's another question for you. We got a rental car because it was only $8 more for the week when we booked our stay and figured it was cheaper than hotel transfers so we did it. We don't plan on driving too many places there but do you think it would be better to try to drive to Chichen Itza instead of riding the bus or by private tour? Or is driving too risky?
We have only rented a car on Cozumel which is a heck of a lot different than the trek from Cancun to Playa which we have only taken with a private driver. I would be intimidated by driving that myself.I found this resource which may be helpful to you: Driving in Mexico and the Yucatan I would love to hear from those who have driven it!