If you decide to go with Mac, you'll have a whole lot easier time integrating all your different audio/video applications. For insance, all the iTunes, iPhoto, GarageBand stuff is included for free on every Mac and they all work together like one program. To get all that stuff separately on a PC would cost over $1000, plus you wouldn't be able to integrate any of it.

As far as using recording software goes... I'd choose a Mac any day over a PC. I've got both and I can tell ya for sure that I use the PC as little as possible. My Mac is about 9 years old now and is still running OS9 and it can outperform a brand new PC running Windows XP.

As far as Firewire vs. USB. In my experience, USB is extremely sloooow.
I bought an external usb drive and it won't even run my recording software.
Plus, copying files takes about 4 times as long.