If I could choose a mentor, I'd still choose Sean Kernan (as I did Years ago at the Maine Media Workshops).
Why: Because Sean is a model for championing creativity as both a mindset and a process. His commitment to exploring how to get into "the zone" where fresh seeing and fresh execution exceeds our usual parameters and abilities. With that as his focus, he "teaches how to fish", and that's inspiring to me in my own mentoring.
Aside from that, he's also a great natural appreciator of other people's work when it shows both personal growth and images that have "Life" in them.
In the original workshop I took with him, he also gave a model for feedback which I use, to this day, when asked for input/critique; the basic idea is to give feedback about what I see in a mentoree's work, not advice about how it "should" be. The technicals might then be useful in tweaking the vision, instead of being more important than vision. See what I mean about his focus? At least that's what rocks about Sean as a mentor, for me... and I'm not alone, based on many Many students of his workshops.Sean's Journal: http://seankernan.squarespace.com/
**I have been wanting to add a key mentor to this post: Me. Rather, my intuitive "knowing" self, which usually is only present when I connect with a subject in some unusual way or depth. Maybe a better way to put that is that my other best mentor is a connection --a "we", as opposed to separate "I" and "subject".
In that Zone that I refer to, above, such a connection comes more easily and has a more organic evolution. When I am willing to be open and to engage in the "dance" or "dialogue" with what's in front of me, using my camera as a lover uses a caress, both giving and receiving creative energy, then something is revealed in the resulting image(s) that neither I, nor my subject, could make alone. I get to trust myself, and trust my subject, and trust our connection to guide me into a fresh adventure.
Then, a Third mentor becomes the viewer; feedback helps keep me honest, free from being victim to my wishes, beliefs, opinions, and blind spots, by letting me know what has been transmitted to the viewer. An added bonus is that feedback shows me what might be in my own work that I wasn't yet capable of seeing.