what do you think is the best thing to use for chesscom? mouse, trackpad, or touchscreen.

neither! trackballs suck for any and all purposes! a wireless optical mouse period!

on a tablet the touch screen is often good

Completely agree but in other daily games is the best. 

1000% the fastest

Touchscreen. I play from mobile, usually rapid. Blitz gets harder tho

With trackpad I too often have the issue that I'll try to move a piece, and then somehow it goes into a mode where it's moving the browser window and the piece stops moving. From this state I don't know how to avoid dropping the piece at the square it happens to be over. This doesn't happen often but often enough it's cost me multiple games, since typically this drops the piece adjacent to, or at least within attacking range, of a piece I was trying to capture. It's super-annoying.
Of course mouse slips are a thing as well.

use a shovel

I use my little dog paw

😉

A touchpad...