This is very difficult for other people to answer. You have to answer this for yourself. For example: from my 2 weeks of living with Windows 8.1 as my only OS, I say Windows 7. I had slow load-times in File Explorer (icons and thumbnails took a long time to show up), and I had this irritating problem:
I also hated how Task Manager never remembered the tab that I was on last (I prefered the Details tab because it was identical to the Processes tab in Windows 7, and I also hated how if I wanted to see the number of processes running, then I'd have to switch to the Performance tab. In Windows 7, I just look at the Status Bar. So, there's no Status Bar in the Windows 8.1 Task Manager, so you also can't just quickly glance at it to see your CPU usage and memory usage either.
Personally, I use and prefer Outlook and Word 2003. While Word 2003 works flawlessly in Windows 8.1, Outlook 2003 has some extremely minor issues (well, I think they're minor): no mailto. Yep. You can't assign Outlook to mailto in Windows 8.1. Outlook 2003 also has a type of "auto complete" feature for typing previously-typed e-mail addresses into the To/CC/BCC fields. In Windows 8.1, the suggested e-mail addresses come up, but they cannot be selected. You still have to type the entire e-mail address. In Windows 7, they CAN be selected and so that means I don't have to type any more than the first couple of characters.
Other than that, I think I loved Windows 8.1. Seriously. If it weren't for these issues, then I think that I'd have purchased it already because after installing StartIsBack+, Gadgets Revived, and Old New Explorer, I had everything I wanted (and then some).
Regarding mailto for Outlook 2003 in Windows Vista and Windows 7: this is just for anyone reading this who has Outlook 2003 and wants to get Mailto working in either Vista or Windows 7:
The OL2003Fix file is what did it for me. I just run the file and at first it seems like nothing happens. However, opening Default Programs > Set your default programs shows what happened: it added "Microsoft Office Outlook" to the list! So, you have to click it, and for peace of mind, click "Choose defaults for this program". In there, you get to enable "MAILTO"! :)
Edit: OMG THIS WORKS FOR WINDOWS 8.1! I just tested it!
Edited by TwoCables - 4/24/14 at 8:41pm