[moh_maya]

Something from the OnePlus series, which, if you are comfortable with rooting, you can install a custom ROM and keep getting updates.

Alternatively, you could perhaps buy a nexus 6P? It's on amazon.com now for about 300$.

[iKlsR]

I have my OnePlus One from early 2015 which is my daily driver, swapped in a new battery the other day and I'm good again. Sadly they seem to have abandoned it entirely tho, haven't seen an update or anything in over a year. Performance wise however, I don't see myself switching anytime soon.

[moh_maya]

Yeah. The OnePlus update rate is lousy. But in terms of value, it's hard to beat..

But there are good roms available [1], and rooting is not all that hard. So that may be an approach you could try?

[1] https://forum.xda-developers.com/oneplus-3