I ordered my chicks from My Pet Chicken, but I had a small order (minimum shipment size=5 bantams). Only 60% survival rate out of two shipments... which I mostly attribute to the long shipping distance across the country.
I had mixed experience with the customer service... Since more than half my first shipment was lost, they do a replacement shipment, and said they would call me the next week to arrange. But they did not call me; instead scheduled a smaller than minimum order, containing types of chicks that didn't match the ones I lost, for a week I couldn't receive them. Luckily, I got suspicious and called them, and managed to get it all sorted out before the order went out. But they did refund for a chick that died in the second shipment, and also refunded for one who turned out to be a cross-beak, who is still doing ok.
My chicks are still a little young, but they all seem to be girls, as claimed... which is exciting because one of the main reasons I ordered from MPC was to get sexed bantams.
Just my two cents. If I get chicks again, I think I'd try to find someone local, and avoid USPS.