Pixel not necessarily the smoothest though check out MKBHD video on the pixel and why he stopped using it. For some odd reason, the pixel started to slow down and it happened on a brand new pixel too.
But yeah generally, animation etc smoothness oneplus seems to be one of the best Android if not the best. Android One phones may be good but I'm sure they stutter too as they're on lower end hardware.
This pocophone should be better than any XiaoMi that isn't using the 845. 845 is a flagship and should perform better than even those on Android one.
Of course one way to reduce stutters etc is to just off all animations