I would say that this depends on personal preference.
650 has AMOLED screen.
The 830 is supposed to be the "affordable flagship" so that one probably wins for the best main camera.
The 650 wins for the best front facing camera.
The 830 is the only one with physical buttons.
Btw, the 640 and 830 have the same processor.
So we need to know, what is important to you?