Minecraft wiki entry for Player_versus_Player, associated text: Size: Bigger may not be better, as a visible structure gains visibility the larger it is, and leaves more space unguarded. On the flip side, big bases are very good for large amounts of people that are working on something together, and can hold more munitions. A small base is also dangerous, because it will be very easily demolished.
Type: One effective type of base is a base that is deep underground. Here enemies will take days to hunt you down, while you survive on a farm and branch mine for diamonds.