I like Windows 7 since most games and newer software these days are made for Windows 7, and some don't work on XP.
But, XP is a nice and light operating system which runs smoothly even on a single-core 1.6 GHz CPU with 512 MB of RAM, and a older video card like the Nvidia GT 620.
Deifently windows 7, more modern, more software for it and easier to use not to mention it has many more features to it.
Windows XP is will commonly used by a lot of British companies like the NHS due to it's ease of use and server capabilities but I still prefer Windows 7 though in my mind windows 10 is the best 😉
Windows 7 is basically a slightly better version of XP. Hard to get on a new machine now, but you can buy a disk of it off of amazon (called an OEM disk I think).
Windows XP was a really nice software, but I live for more updated versions of softwares, so with that, I have to go with Windows 7. It's more secure and updated overall. 😛