I use Large.
Huge setting is unmanagable( at least for me ), and have serious lagging problem. My system : P4 3.0c, Radeon 9600XT, 512MB RAM. It's ok unless two large armies start killing each other. When the battle is nearly over, fps was dropped to almost below 10( didn't measured exactly ). I don't want sacrifice any graphical settings, so I use Large.