Regarding Lubiner & Schmidt, I know of 10+ people who got RIR labor and I-140 done in 4-6 months. They are good.
My experience is that just because a lawyer is not comfortable with AC21 doesn't make them bad. Honesty makes it very straight forward. I've heard of lawyers who take cases just to hook the client, collect their money and then get tangled in such a mess. I'd rather go for a lawyer who is straight forward and honest in their approach. Its the ever-confusing INS laws which are not clear-cut to begin with.
Native-born lawyers do have more connections inside the immigration circle and so, they have an edge over lawyers who are immigrants themselves.
Finally, don't ever go to a lawyer who is into all types of legal cases (divorce, civil, real-estate etc). They have too litle info on immigration and it will be a total disaster. Check with AILA.org on lawyers who are currently in immigration practise.