I have been using EM for 4 years now and have recently started doing Senior Portraits. The Quality from EM has always been great but I wanted to compare the portrait prints with those from MpixPro so I set up an account and sent them the required test prints. I was expecting some difference since EM uses Fuji Paper and Mpix Pro uses Kodak. I had to look very close to notice any difference and the slight difference was more about personal taste than quality. When I asked other family members to choose which one they liked, it took them some time to notice any difference and then they chose the EM prints.
One thing that disappointed me about Mpix is that one print came back with a vertical mark running down the print (maybe from a printer roller?) The packing slip was stamped "Inspected by....." It makes me think that the only inspection is to make sure the proper prints are packaged. I would have thought that "test prints" would be perfect before being shipped.