Xorg-7.7 is preferable if you have a slow cpu, relatively little ram, not much storage space for extensions or no need for accelerated graphics.
You might want to keep Xorg-7.7-3d for occasional use, in which case you just need to check that it is not listed "onboot", reboot and load Xorg-7.7.
Otherwise, start the apps gui and use maintenance/dependencies and deletions to mark it for deletion.