There is NO comparison when it comes to MAC and PC. I used PC for my Graphics all throughout my life, then switched to MAC 5 years ago. Once you go Mac you NEVER go back!! Mac is just a MUCH more stable OS than Windows will ever be, and it's faster. Yes, much faster. My macbook pro has an i3 processor, and my design computer at work (PC) had an i7 processor, both 2.9GHz, both 8GB of RAM. My MAC blew the PC out of the water with a test on opening a large file (500MB) in Illustrator CS5. Again, same program, same file, but the Mac was much faster. This is due to the OS, nothing more than that. Mac OS always has been, and probably always will be a better built machine than PC, and the price tag confirms that! LOL
Many other people will share a different opinion, as you've seen, so I really think it's just a matter of preference. I also LOVE the easy syncing between all my devices. Yes, you can do that with Windows to, after you download 3rd party apps, software, etc., but it's not nearly as "user friendly" as syncing Apple to Apple devices.
I can't comment on Flexi with Mac, I never used it, only on PC. I just use Illustrator with Master Cut 2, it came with my Graphtec, works great.