Minecraft wiki entry for Multiplayer_PvP_bases, associated text: Very hard to find if put a good distance from the spawn point (around 250-500 blocks).
Water shields are possible (better than Nether base).
Similar to Sky Base (endless void down there).
If you are strong enough you can control the return portal and force others to give you their stuff to get out of the end.
Easy access to ender pearls.
Almost everything renewable in the overworld is renewable in the end.