Good/fun strats to beating wave 666 in Mann vs. Zombies?

I haven't had the chance to play other than with pub players but my personal favorite class is Heatmaker sniper. +damage and explosive headshots takes down multiple giant robots with 3 headshots as well as blows up every normal robot around them. Add on focus to that and you become the rapetrain.

If you don't believe me, try it. It's fun and you can put out more damage than even a sentry