From personal experience, some people (i.e. me) are too pig headed to learn from other people. Sometimes it feels like a step down to take on a mentor. Sometimes it feels like the available mentors are all so far behind you that there is no point. But there is a real danger of getting isolated in a local maxima and not being able to jump across to somewhere better. Sometimes you have to lower yourself in order to go higher.
I once had a good manager who explained to me that perspective is like looking at a room through a small window. You can only see part of the room. Other people are looking through other windows, and likewise can only see a small part of the room. In order to see the whole room you need to see what the other people see. You have to go where they are and look through their window. It's the only way to piece together the whole picture. Even if you have the best window and the best vantage point, it's still better to give it up for a while and take a look at the other vantage points.
So, it doesn't really matter who you pick as a mentor, except it should probably be someone who sees the world differently than you do. And it will be really, really annoying for a while (maybe a long while) ;-)
I've been successful in my career but maybe I'm leaving something on the table?