If you want a fancy case get a mac.
If you are looking for raw performance get a pc. The components in both are the same only the mac has a fancy case. I recently bought a Samsung NP350E7C S02UK as its the only laptop with a i7 processor 8GB of RAM and 4 USB ports(2xUSB 2.0 + 2xUSB 3.0) Which covers Ableton Push, APC 40, Vestax VCI380(Serato+Audio Interface), and one to spare for my AVID Eleven rack for Protools when Im at home.
There simply isnt any other laptop with those specs, and it only cost me €800, and I had a €10,000 budget.
I work in IT by the way and have seen more issues with Apple's than PC's, plus you get a right mouse button with a PC. Saying that both will run Ableton smoothly. The best processor and as much high speed RAM as you can get. If you can setup a RAID 0/10 array with 2 hard drives is even better, and if you can get a large SSD is better than that. No point getting loads of RAM if you are not going to use 64bit Ableton though, and Max4live is now 64bit too.
Just remember fancy case doesnt mean better. It also doesnt mean worse, but it usually means more expensive.
If you get a PC ahead of a MAC you have more freedom to do what you like to it, but that also means that you run the rish of cluttering it up with crap too, so you need to be more careful as you have more freedom with a PC (Buy your software, close your antivirus+firewall when performing, disable wireless also, etc)
If your getting crackling and your CPU is not getting hammerred then you should try a different USB cable. If not that then you should check your sound card (use an external one)
Hope that helps