I'm surprised no one else has tackled this yet...
Well I've had the luxury of working on both Mac's and PC's on both Pro Tools and other programs.
Sound Quality... Both are the same... because it comes down to your sound card i.e. Recording interface.
Machine wise tho basically it comes down to money. People will argue Mac's are more stable and PC's crash and blah blah blah... What it comes down to is money.
If you are on a budget to build a recording setup. I would say a PC. They are upgradable. Mac's aren't as friendly when you are adding more RAM. Forget about upgrading the CPU, unless you can afford a Mac with an Intel CPU.
I would honestly say, if you can work with a Desktop do that... MUCH cheaper then a laptop More Processing Power and more Storage.
If you get to the point where you can afford an expensive machine, COOL! But I would honestly build a desktop to save the money, and invest in some better mics, mixer, sound card/interface or whatever other tools you need.
If you have any questions, or don't fully understand I have a good amount of knowledge for this kind of stuff. You can e-mail me directly PatRock1983@gmail.com I'd be glad to help you.
If I can't answer your question I can at least point you in the right direction.