Irrlicht Engine

so I'm running Ubuntu, and I've got both the VidMode and RandR X11 extensions installed. Is there any significant difference between the two? Should I compile Irrlicht with only VidMode, only RandR, or both?

If you use both there's a broader support of systems for your app, because any of the two extensions would be enouhg for fullscreen support. However, xvidmode has only limited support for screen changes, and seems to become deprecated. So unless you want to support even very old systems xrandr should be enough.