A coach, a mentor and a fellow entrepreneur aren't the same thing.
A mentor has the mission to make you gain from her/his experience but will always have an insider's position.
A fellow entrepreneur as well will be an insider and will also give you feedback from his point of view.
The coach (if proper coach) will help you pick your brain to determine the best course of action and will help you evaluate the situation without bias.
I'm a coach and I'm partial of course but I do think that all 3 have their use and their limits and shall be used complementarly.