It's up to you, but from where I'm standing, it looks like the $800-$900 Pixel 3's reign as the top smartphone camera is put under heavy strain by a phone that starts at $550.
The Pixel 3 and the OnePlus 6T take very different types of photos.
The Pixel 3 creates photos that keep dark areas dark, which can sometimes make for deeper and more dynamic photos when contrasting with brighter areas of the shot. The result usually looks better than the majority of the competition, which is why the Pixel 3 is often crowned the best smartphone camera.
The OnePlus 6T wants to brighten up darker areas to reveal more detail, which can be hit-or-miss with certain smartphones. Samsung's Galaxy S9 and Note 9 try too hard to brighten up darker areas, for example, and it often results in a flat, less dynamic photo. However, OnePlus seems to have figured out a great balance, and the photos look stunning for it.
The OnePlus 6T didn't always work out better than the Pixel 3, but for this trip, I was happier with the OnePlus 6T than I was with the Pixel 3.