I have to say I'm impressed with Windows 10 so far. Everything worked straight out of the box, no driver hiccups or programs not working. The GUI looks very professional and its a major improvement on Windows 8.1, on Windows 7, perhaps less so, but looks like the font rendering has had some improvements as text looks sharper to me on my 27" screen. Also feels faster than Windows 7, but it could just be the replacement SSD I chucked in.
I have my doubts about the quality of Mac OS X, new OS releases never go without some issue. I always try and wait a couple of releases before upgrading, but to my regret abandoned that strategy with Yosemite, which gave me endless crap on both my Macbook Pro and Macbook Air. On my Macbook Air the Wi-Fi would disappear for no reason at all and wouldn't come back till I downgraded back to Mavericks. The OS was very laggy on my Macbook Pro until they made a couple of updates. The flat GUI style also didn't look at nice as previous versions. It took about 6 months for the entire thing to smooth out. I sincerely hope El Capitan is going to be a better launch so I can finally upgrade the Macbook Air from Mavericks. Given that Apple only have to optimise their OS for a limited set of hardware platforms its a bit perplexing that the QA is so bad.
I have now sold my Macbook Pro as I cannot run professional applications on it and running virtualized apps was an unstable and buggy mess using Parallels 10 and they come begging for more money every year to fix the bugs of the previous version and then introduce new ones so you are forced to upgrade once again.