I have the Waterfield bag (Cozmo with a couple of organizer pouches); as well as the Mini Roadster that I got from RedOxx. So AVService, here are some of my thoughts:
1. All of them are built like tanks; there is no doubt about it. They use excellent materials, and their craftsmanship, although very different is outstanding compared to the usual run-of-the mill bags.
Having said that, I am less sure about "design." I follow design--and Yvon Chouinard, who founded Patagonia, used to say that "form follows function" and that a good design was one where there was no detail that did not have a function or a purpose. That all parts of the design worked seperately and together. The early Patagonia designs were built on that philosophy; I can't say their current designs do.
From that POV, the Waterfield designs are not as thoughtful as TB bags can be. The briefcase (Cozmo) is far far superior to the average briefcase; and their shoulder strap comes close (but not quite) to the Absolute Shoulder Strap. They are also more stylish and will perhaps fit better in slightly more corporate worlds than the TB briefcases. But it is the small thoughtful design quality that sets apart TB: the just right pockets placed exactly; the mindfulness that has gone into the Western Flyer's different pockets in front so that they all function as they meant to without bulging one into the other.
For everyday use, I find TB more "functional." I do like the style and quality of Waterfield bags, but they are not as multipurpose as the Imago. That is another distinguishing characteristic. For example, I have been able to use the Imago as a daily messenger bag for school; I have also been able to use it as a gym bag of sorts; as a second carry on with the Western Flyer; even as a grocery bag! I can't do that with the Cozmo --which functions only as a briefcase. I realize it is NOT meant to function as anything else, but most of their products are somewhat UNI function--if you get what I mean.
So that is my two cents!
I will say that the Waterfield Kindle cases are extremely well made, and perfectly designed.