For *my purposes*, both Blurb and Magcloud are giving me good and consistent results. Caveats, of course:
(a) For Blurb I use the "color managed flow" which at some point was available only in their B3 Business-to-Business program. That may have changed now.
(b) The work I had printed tends towards grainy, soft-focus, not-a-lot-of-detail look ( see
http://www.jonasyip.com/paris-dialogues ). I have no idea how a highly detailed, exactingly color-balanced image will print.
(c) The work is monochromatic, but with a *brown tint*. Holding both versions in front of me now it is clear that the Blurb and Magcloud versions have slightly different tints. However, either version is fine on its own, and more importantly both have been *consistent* over multiple printings. Point here is that I don't know if either party can produce a perfectly neutral black-and-white, if that is a reqiurement.
In any case, it's cheap to try Magcloud and see for yourself since you get a free proof copy of the full "issue" just paying for shipping ($1.20 or something).
j