After experiencing the awesome display of black levels in my JVC PJ, I would say that the best picture quality (colors, black levels) within your budget is salient, not the 4K resolution, which I think is mostly for bragging rights.
Reliability is always salient.
Based on my experience with a $5,000 (MSRP) brand new Optoma DLP PJ, I would avoid Optoma like the Plague.
For less expensive PJ, I would probably look at Sony, BenQ, Epson, and Vivitek.