I'm only upgrading to Windows 10 when I build a new PC. I don't feel like there's any real benefit to upgrading my current PC, plus the shock of the transition might kill the old girl. The only real reason I'd even use 10 is DirectX 12 (which doesn't even matter with my current PC and probably won't matter for a while anyway) and the fact that it's still getting updates. Overall I feel like I'm downgrading but what can you do?
I remember I was really early getting 7 since I got a new laptop (Inspiron 1545... could barely run TF2 but it did and that's why I'm here today so it gets a salute from me ;_;7) and it was really neat since I had only used Macs and school computers I couldn't do anything with before. Good times, 7 was what all products should strive to be. Probably the best thing about it, to me, was it felt modern, but it wasn't trying too hard to be modern like a lot of software today.