So I've been using the OnePlus 3 for the past few days (coming from a 6P)
- The screen, while having a very blue white balance, is completely fine. I definitely don't think it's bad by any means. It's clear that the calibration is off, but I thought, for example, the Nexus 6's screen was significantly worse.
- Performance is good, but it's really not worlds apart from the 6P. In fact, the 6P's screen feels a tiny bit more responsive to me. Faster touch response maybe? That said, load times for apps are faster on the OP3, but only by a second or two.
- I love the build/form factor of the OP3. It's lighter than you would think it would be, but not so light as to feel cheap. The bezels are tiny, and coming from the 6P it feels significantly smaller in my hand, even though the screens are almost the same size.
- Wi-Fi performance is awful. I guess that's an area that OnePlus cut costs, but I noticed when downloading and updating my apps that speeds are much worse and more inconsistent than the 6P. Also, the OP3 really likes to lose its Wi-Fi connection when it's dozing. Even when you turn the screen back on, you often have to turn Wi-Fi off and then on again to regain connection.
- The OnePlus 3 definitely runs cooler than the 6P. After ~30 minutes of web browsing on Chrome, the 6P is noticeably warm, while the OP3 is almost completely cool.
- The fingerprint sensor on the OP3 is the fastest I've ever used. Much, much faster than the 6P (which was already pretty quick).
- Battery life on the 6P seems to be a bit better, but not by a whole lot.
- Personal pet peeve: you can't play HD videos from Google Play. They only play in SD. Why.
Overall, the 6P feels like the more polished product. Plus you obviously get better update support from Google than OnePlus. But the OP3 is quite a bit cheaper, even with sales for the 6P.
Honestly my original plan was to sell the 6P and use the OP3. But now, I'm returning the OP3 and keeping the 6P, at least until the new Nexuses drop.