For print applications where sanding is to be used to reduce the appearance of layer lines on medium to large objects with sweeping curves, but little to no surface detail (A vase or cosplay helmet, for example), which filament type offers the best finish?
You may discover that the type of filament has minimal bearing on the surface finish. PLA melts at a lower temperature than most of the other filament types. During sanding, it can melt into and clog the abrasive media if sufficient heat develops. This can be mitigated by using wet/dry sandpaper or applying water periodically during the sanding.
I have found that ABS and PETG are less prone to this problem. If your only objective is to remove layer lines, you may accomplish that goal without wet/dry abrasives. If you desire to have a smoother finish, finer grits will require the wetting of the surface.
As higher grits are applied, one can develop a near-glass-smooth finish. I have used this process (including micromesh™) on both PLA and ABS resulting in reflective surfaces.