It depends on what kind of advice you are seeking from a mentor.
Dominants make good mentors for some advice, but I would also seek out other submissives who can offer up thier own words of wisdom.
They have more than likely already been there and are better equipped with information on how to handle difficult situations.

I won't reiterate what everyone else has already said, but I would follow up on lily's advice.

Only you will know by talking to others how comfortable you feel with them.
Also don’t just find one mentor, ask as many as you feel comfortable with. Everyone views things differently and it is better to have varying opinions that just one individual one.