I love the WW1 arena.
Success in the MAs I think are due to the fact that there is an objective involved.
The simple hatred for bomb****s, toolshedders, NOE hordes, milkrunners are what keep the MAs alive and hopefully soon, some sort of objective is incorperated into the WW1 arenas to keep player's attention span focused in there a bit.
As it stands now, I frequent the WW1 arena. Although great fun, I do tend to get bored after a few sorties