With PowerPC's you only have older versions of Mac OSX and Linux
This is the best operating system for most G4 machines. It has good application support considering the fact that it is more than a decade old. Apps like Photoshop, Final Cut Pro, Spotify... are all available here. The only app i miss on here is WebKit but i can live without it with no problems. It has a bland and boring design compared to Leopard and features like Time Machine and Spaces are missing but other than that it is a good os that is more than usable if you ask me. It runs smoothly on all G4 and G5 systems (its buggy and slow on G3s) but if you have a beefy G4 or a G5 i would reccomend using Leopard (just to be as up to date as you can).
This OS is best left to G5's. It is demanding and performs terribly on slower G4's (It is not supported on G3's) It has all the fancy features and app support is not a problem on it. The latest update PowerPC's can run is 10.5.8 and no further. I really cannot reccomend this OS in any way, the best reason anybody can have for installing it is just to be up to date or because of the fancy design. Other than that Tiger performs better in every way
I cannot really tell you what to do with this one... Mostly because i have not really tested it as much. Ubuntu 12.04 ( IIRC it is the last version that is supported for PowerPC), that is the only version i have tested and it runs slowly and it doesnt have good app support so i do not reccomend it. HOWEVER Lubuntu and Ubuntu MATE also exist, lubuntu has a much newer release (16.04) and i also believe MATE has a 14.04 release from 2015, but it is only a matter of time before these lose support and become useless..