I've used xrack & itsamac, the service from both was ok. Never used serverlogistics, but I do know people who have and they were happy. Personally, I've moved all my sites to a company called ASmallOrange who hosts on Linux based machines. A lot more bang for the buck, and the service is great.
Just remember, in general, you will pay a premium for Mac based hosts. If I had to pick one (Mac based), right now I'd lean towards serverlogistics.