Overall dimension they're the same unit. As to build quality I haven't been in a 17QB unit so I can't verify if it's better or worse than the 17FQs. I would suspect they may be built in the same factory as it wouldn't make economic sense to build these very similar units in two locations.
The different bath arrangements both have pros and cons. The 17QB does gives you more hanging storage and additional outside accessible storage. But I don't like the small sink stand as there's little room even to set down your toothbrush. In the 17FQ the vanity style sink gives you more room for what I consider bath items. And from the pictures the 17FQ has more room in the bath area for maneuvering.
Galley and dinette are pretty much the same, with just some things - refrigerator mainly - moved around. Up front the 17QB lacks the large window on the front of the 17FQs. I've found that window lets in a lot of light to the camper so I consider it a plus.
Another difference I saw in a video for the 17QB is that they leave the under bed storage area open to the front pass-thru storage area. I use the front pass-thru storage for "grimmer" items like lawn chairs, mats, etc. So I prefer having the separation with the under bed area. Again that's personal preference.
Barry, MSgt, USAF, Ret. & Rose
2015 Nissan Frontier V6
2014 Coachmen Viking 17FQ