If it's Arca-Swiss you want then why not go with the original? See my review here
. From memory, while I was considering my own purchase I got the impression that the Kirk Photo units are well regarded, though in the end I only bought one of their plates for my 40D. The alternative ballhead that I was closely considering was the Markins Ball Head Q-Ball Q3 Emille
but in the end the Arca-Swiss Z1 DP Ballhead won out.
has some wise words on his site regarding ball-heads, though the article I linked to there is more about tripods.