I'm the opposite of a lot of the others, I guess. I left Digidesign (Digi 002) for MOTU (828mkII). Both are fine products with weakness and advantages, I just became limited with the Digi 002 route. I think it comes from it being initially designed to work as an all-in-one sort of "bundle unit" (mixer = interface) for ProTools, that lead to me leaving it. I wanted something truely expandable and "open", being able to work with ProTools, then, became unimportant completely.
Basically, whatever gives you the best workflow, sound and comfort, is the best.
The difference in sound quality between the Digi 002 and 828mkII is not the gear, it's the producer/composer. Both are up to par. As for ProTools, it has like 20 percent to do with the sound, as opposed to the inputs, A/D and the other gear, which has much more affect on the quality. Unless you're comparing to some consumer level stuff. Digi002 + LE/TDM vs. Motu 828mkII + Cubase or Nuendo or Logic....the result comes down to you, and your abilities. But, that's my point, how would we know, when the 002 is designed for ProTools exclusively? If the inputs are good combined with good software, we assume it's all good right? So, if you take an equally good unit like the Motu, and say Nuendo, then we assume it's all good right? It's preference.
It's just more often than not that we say "wow' to Digidesign stuff, because it's guaranteed compatible, with ProTools, while Motu is open, and can use everything, which may not work. Not to say it's not good, because it is, but a lot of people also glorify ProTools oriented stuff, because it is the most used. It's the Micheal Jordan shoe of audioware, if you will, an elistest's ego boost for many. Try for yourself, and don't be biased.
Both are good.