Perhaps Empire w. a pure gunline list. But then ... there's nothing I'd really be afraid of facing. I can only try my best with the army at my disposal at that moment. *shrugs* Sometimes one wins, sometimes one doesn't.
There is no real army I fear facing but there are some that annoy the hell out of me.
The army I hate facing the most though is Chaos Dwarfs, magma cannons and destroyers just ruin my day. Granted i still dislike things like Unbreakable Deamon princes etc but nothing is more annoying that watching a horde or a unit of cav get hit by a magma cannon template.