I have printed hundreds, actually thousands of images at MPix, via Zenfolio.
I think the quality is very, very good. Any time I have had issues with the quality, it invariably has been my own fault (bad color on the file I sent them).
Three observations on photo lab testing:
1. Any testing done as a "one-off" is likely to produce unpredictable results -- bad labs can have good days, good labs can have bad days -- there is NO perfect lab. So don't trust testing that isn't run multiple times over several weeks or months.
2. With all due respect to SmugMug's testing -- Bay Photo is a financial partner that is an integral part of SmugMug's revenue stream. Without wishing to suggest that SmugMug is cheating - let's face it -- don't all of us prefer to get our testing done by somebody with no financial interest in the outcome of the test?
3. This whole lab testing business is a bit like comparing two very similar cameras. When I hear somebody getting all religious about the superior image quality of their camera vs. another, I always ask a simple question: would you be willing to let me put a gun to your head, place a stack of 16x20 prints before you, and ask you correctly guess which is taken with say, the Canon 7D, and which with the Nikon D700? The SECOND print you guess wrong -- I pull the trigger.
I wonder how many photographers would be willing to do this?
My opinion is that the differences between two excellent photo labs are about the same. One may be slightly better or worse some, or even most of the time -- when critically viewing comparative prints. The question is, is the difference big enough to be meaningful in the real world of commerce?
To me, MPIX quality is truly excellent, and their service is irreproachable. And despite the large volume of prints I push through MPIX, I also use a couple other reputable labs every month just to keep tabs on the world -- so far, I've seen nothing that makes me think using MPIX is anything like a poor choice.
Best,
Paul
http://upstatephotographers.com