The largest G4 iMac had a 20" screen. It looked a bit top-heavy but it worked fine.
https://upload.wikimedia.org/wikipedia/commons/8/85/IMac_G4_...
The 20" definitely looks the least balanced (aesthetically).
Only trouble was the fans were ridiculously loud.
Firewire connectivity for external hdds was magical. The screen is still nice. However the fan noise is and was always terrible. With some mods it became bearable.