There are lots of attorneys that range from those that wrote the book on immigration to the truly incompetent. Whoever you chose I would recommend ensuring that the attorney is a member of the American Immigration Lawyer's Association. I feel that membership is indicative of the amount of immigration law the attorney practices and it is difficult to handle lots of immigration cases without being a member. Due to the frequent changes in immigration law, years of experience is probably less important than AILA membership. Of course, the attorney (AILA member or not) should have a certain amount of immigration experience.
Word of mouth is certainly the best way to choose an attorney.