Hi Jane
The Gran Bahia Principe resort consists of (from the North) Tulum, Akumel and behind the Akumel, the Coba.
There was a fourth location on site which is the Hacienda, where there are shops, bars and a disco.
All the hotels are serviced by buses and you can freely move around and use resources at any one.
We took the decision to stay at the Coba because all the rooms are junior suites, and it is the quietest hotel. The Tulum and Alkumel are on the beach and so whilst their patron move between them, they do not go back to the Coba, whereas many of the Coba residents do go to the beach, or the other two hotels. There is plenty of entertainment from the team but it is nice and quiet.
The Coba buffet was supposed to be the best of the three, but a couple we befriended always went to the Tulum for their breakfast. The A la cartes are available to all but you have to visit each hotel to find out their existence and their menu. ie in the Coba they told us there was no steak house, but when we found it and asked to book it by name, they did straight away.
Evening entertainment is slightly different in each hotel so can be worth popping round, I assumed they would cycle between the three but when we went to the steak restaurant in the Tulum we stumbled upon the entertainment and found it was a different show we hadn't seen so we started going there in the evenings.
Slight problem with the complex is that it is geared to a weeks stay and so the second week is a repeat.
A bus stop down the road is the Xel Ha park, well worth a day out using the bus or a taxi.
The beach at the Tulum is probably better than the other part of the beach, but you can go where you want and there are bars there for drinks, one even has swing seats so you don't know when the world is swinging on its own..
Up to the North is Akumel village (I think) where you can go to the public beach and swim with turtles for free.
Further North past Puerto Aventuras is Xcarat, another good but expensive day out.