We took the bikes at Coba, after not having been on one in 50 years, and it was a little scary at times, but I never hit a tree. There were several busloads of tourists there, and it seemed that most walked, but biking was best. I should have taken a name tag for mine. We'd park our bikes at times to walk around a ruin, then go back to the group and take one that looked familiar.
Tulum is an interesting & lovely small ruin on the coast. I just got the feeling that is was overly manicured. Some of the bikinis going down the steps to the beach were hot.
Chichen Itza is great if you spend the night nearby and go in early, then leave before the hordes arrive by bus. Nearby Ek Balam should be included if in the area, going there after Chichen Itza.