I had a computer built for me not long after windows 8 had been released and went for windows 7 simply because at the time there were a lot of negative comments about 8. To get one built was a real leap of faith me because I am not technically savvy at all but it was the best thing I ever did as it came without any of the unnecessary c..p that comes with on the shelf buys.
Windows 7 was a known quantity for me and I'm not particularly quick when it comes to new technology so at the time I was happy with my choice, but if I was buying now I think I'd go for windows 8. This may have something to do with the fact that I bought a new windows phone not so long ago and have had no problems at all getting used to that.
I hate windows 8! At work I sometimes have to use windows 8.1 and I really dislike it. It also seems super sensitive to our broadband link being weak at times and I often have problems getting on the internet. The PCs running windows 7 are much happier! I use an iPad a lot so I am not opposed to change but windows 8 is a change too far!
Yu mention nothing about past usage, but if you're familiar with Windows XP or Vista already, I'd suggest Windows 7 may be best to go with...
Win 8.x was designed with mobiles, tablets and touch-screen desktops in mind, and while it no dobt works fine with mouse and keyboard, some things were awkward for new users. Don't use it myself, but a friend teaches about technology to retirees, and is looking forward to Win 10
Windows has changed since Win7 and it's not going to be changing back to how it was in the future. So really, not moving with the times now is just going to make the leap harder later on.
Personally I always quite liked Win8, you could see what MS were trying to do even if they didn't have it quite right. But the 8.1 update, although fairly subtle for the most part, makes a huge difference to the experience. If you have tons of experience with XP then you'll get on just fine with 8.1.
Must admit I didn't try downloading the trial version of Windows 10. I really ought to, just to see which bits of hardware can use it, and if unsuitable, time to switch them to Linux, perhaps, before that goes all 64-bit and cannot be used either...