Well, I'll agree with Notes that, at least for now, the PC version of BIAB seems to be a better program. As for the other points he makes, I don't think they are necessarily correct. Macs are a fine machine, easy to use for a moderately computer literate person (same applies to a PC), have always had the GUI as a front end and are not so much more expensive as to be a major factor in purchasing decisions. If all else fails with getting a deal on the Mac version of BIAB, the Mac will run the Windows version pretty well until an upgrade comes along that makes it practical to go with a native version.
I'm a forever PC guy, never owned a Mac, but have used them during my working career as well as doing stuff for my wife on her Mac (until she switched to a PC). A very good computer.
Go with the computer you want and then make it work for you, especially if you are going to use other programs besides BIAB.
Good luck.