The build quality of Carada is significantly better than Focupix and Elite. I have not touched VAPEX yet so I can't compare them. They do a better job with packaging, use a larger roll to protect the screen material, the screen material is very thick and seems to be a better material, the frame is more robust and the surround fabric is of higher quality. The attachment method (snaps) are extremely solid and do a great job of providing even tension across the screen surface without any real chance for error during assembly.
I have worked with Stewart screens and to me the Carada feels far more like a good Stewart screen in terms of build quality, compared to the others. The final projected image looks pretty solid across all the screens though so on more of a budget, I certainly don't have any issues recommending the lesser expensive brands. If you need an odd size or custom ratio, that's one area where Carada can deliver and the others can't.