I have ordered from McMurray for over 30 years, usually 25 layers and 25 cornish cross each spring. I will address my experience based on some of the comments I have seen below.
The customer service I have found to be very good, however, the ladies that answer the phone are order takers and over the years I have only come across a couple of ladies who knew anything about chickens. It is seasonal unexperienced help.
If you want show quality to do not order from MM. I have never had an issue with the health or mortality rates with MM birds but they do not buy from breeders who breed for quality. I can honestly say I have never had a chick arrive dead. Remeber once they leave the hatchery there is a lot out of their control. They can't control a airline or postal worker leaving the chicks sit in extreme tempatures for too long etc. so it does not necessarilly reflect on the quality of the bird.
I order sexed birds except for the cornish cross. This year I did get two roosters (now I have to make soup) but usually the group is 100% female. Oh by the way, I always tell them I do not want extras or the "free" exotic chick, in my experience it is a rooster. I tell them I only want the extra chick(s) if they can assure me of a hen. They usually don't send it.
Order your chicks early. They have a limited supply of certain chicks. I have not always gotten what I wanted when I order say the first of April for a first of May shipment.