I'm not a big fan of MacOS at the moment, overall stability quickly declined after Snow Leopard (10.6), but I think it's still a better alternative to Windows 8. Web development is so Mac-centric now (I'm mostly focused on front-end/UI) , that I couldn't even run Windows if I wanted to. Windows IS still faster at running Photoshop and most web browsers on the same machine.
It sounds like this is for your mom/parents. MacOS would only be suitable if they're willing to learn something new. Most parents/older relatives are not

I'd just go Win8 and make sure they never see the Metro side of things. Windows 8 is definitely faster than previous versions, no point sticking with crusty old Win7.
I installed the regular bootcamp drivers for Windows 7 (on Win8) for a Macbook Pro early 2012 model. No issues. Track pad works with right-click, audio is good, etc. Anyone that's having issues should make sure the drivers from that bootcamp set are properly installed, do it manually if needed and double check everything (go to run, then type: devmgmt.msc , hit enter).
The Metro UI is an absolute joke on something like a 27" monitor, or multiple 27" monitors. It's like Microsoft catered to mobile devices and completely ignored desktop usage. Why would anyone want IE running full-screen at 2560 pixels wide? Metro shows great potential (IMO), but it's a huge liability for them right now.
Microsoft may still have a huge installed user-base, but that doesn't mean they can't become irrelevant regarding the future of computing. I think that's what we're witnessing right now. Our GA stats (for a forum catering to Swiss watch collectors) clearly show that for the middle-class and beyond, Microsoft Windows is already becoming the edge-case minority OS at home.