Right now - brushing!! With four hairy monsters who are all beginning to blow coat, I am now completely outfitted in fur pants, fur shirt, fur hat, fur socks...
Otherwise, it's a toss up between nail clipping and brushing teeth, especially on Ares, because he's so unfriendly about it.
Also, I hate crate cleaning - once a week or so I take the crates outside and cwash them. I hate dragging them up and down the stairs.