From principles: you want to minimize the left right action of your eyes/neck, to reduce fatigue, and not blast your retinas with a wall of white pixels.

One column of centered text with a non-busy black and white background looks great. For a while I read Amazon books like that because I put the online reader in an iframe.

Now I use a HiSense A5 e-Ink screen with a remote control for page turning and I couldn't ask for more.