I've been getting my hair cut by the same person for 12 years now. I look for someone who is friendly, remembers your name and is willing to work with you. A lot of barbers seem to be lazy and only want to give one or two haircuts. I've over the years experienced a great haircut around the edges, but the top was choppy and uneven. Listen to what the customer is telling you and ask them to participate as much as possible. Also let them watch as you cut the hair (facing the mirror). It's not enough to just cut it and show them later on. There's a great article on here about choosing a barber:
http://artofmanliness.com/
http://artofmanliness.com/