You know, the best ones aren't always the most technical ones (and I say that as someone with many many years development experience) - I would ask your friends and community for recommendations, rather than trying to figure it out yourself.

I would also look for ones who are investing heavily in one community. Someone who does exclusively Python in London, sponsors all the conferences, and has done for a while is likely to know which places are nice to work at, where pays well comparatively, and so on.