Heh... again with the "best" stuff, eh?
Picking the "best" ISP is like picking the "best" color -- red? orange? yellow? green? black? gray?
It's all completely subjective. Macs connect to the internet in an identical fashion to PCs -- dial-up, Cable modems (DHCP), DSL modems (PPPoE), etc. All that is built into Mac OS X. There is nothing "Mac-specific" about an internet connection -- they're all pipes to the intertubes, nothing more, nothing less.
Some ISPs have Mac support folks... some don't. If you're the kind of person that's on the phone all the time with tech support, then you may want to look around for an ISP that supports Macs (AT&T does).