I ordered day-old pullets, 10 of them, from MPC 2 years ago, my first chicken-owning experience. I was pleased with the service and selection, and would not hesitate to order from them again. I love that they will ship small numbers of chicks, and that they will sell bantams sexed. If anyone else is doing both of those things, I am not aware of it. (Feel free to correct me, anyone...)
Two of my chicks did not survive their chickhoods--the Silkie died within 3 days and the Black Jersey Giant within about 8 days--both from a "failure to thrive" as best as I can explain it--they just stopped eating/drinking/growing. So not sure what went wrong there or what I could have/should have done differently. My other 8 chicks all grew up healthy and strong and beautiful and friendly (not that I'm biased about them or anything). I got a GLW, 2 EE's, a Black Star sex-link, a BO, a NHR, and 2 Sebrights, a golden and a silver. All were girls just as ordered, even the two bantams. Egg production has been as good or better than advertised. I'm sure these are not SOP or show-quality birds by any stretch, but have served my needs very well. I have heard that MPC's birds come at least largely from Meyer--but if you are interested in bantams and don't want "straight run" MPC is the place to go. (You'll pay a big premium for sexed bantams, but it was worth it to me...)
If anyone is interested in broodiness as a trait (no idea how closely related the MPC birds tend to be so this obviously is just my experience)--the Sebrights both turned out to be super broody and much better egg layers (when not broody) than Sebrights are supposed to be. Proving that MPC chickens, along with chickens from many other sources, don't read the manual too well
(none of my other MPC chickens have gone broody yet, despite some being from more likely broody breeds, but I know it takes a few years for some hens to decide to brood.) The Sebrights first went broody about 6 weeks after laying their first eggs. They would lay easily 5 eggs a week when not broody, though. And super, super sweet and personable birds!
So maybe I just like MPC because I love the birds I got. Since they're the only ones I've ordered from, I don't have anything to compare with. But as I said, I'd order form them again without hesitation...