I am not sure which is better or if there is a better. If you are talking about during exercise and in an environment that is humid and body temp cooling becomes an issue it would seem that colder water would have its benefits. But if you are talking with a meal for general health than I think room temperature is advisable. I do know that colder beverages can freeze the cilia that lines the intestines which will make it harder to digest food.
hope this helps,