+1 for WIn7 x 64. I think I'd prefer to install XP before Win8.

Win 7 64b

If you want maximum compatibility I suggest to install XP and 8.1 in a dual boot, it is twice the work though.

or the windows 7 version that has the xp emulator built in? i know its not quite as smooth as a stand alone install but by all accounts its damn better than a standard emulation?

my vote is for Windows 7 btw. still trying to upgrade the rest of my pcs to it and my newest will have win7 on no matter the cost (wanting a 2nd copy) im not touching win 8 with a bargepole.

Windows 7 professional 64-bit

Get the PRO version because it supports up to 192gb ram - versions http://en.wikipedia.org/wiki/Windows_7_editions

For old games, check out Virtualbox or Dosbox - or even run XP MODE - http://en.wikipedia.org/wiki/Windows_XP_Mode#Windows_XP_Mode

Windows 8 is Jar Jar Binks bad. Rare for me to hate an OS - started with the VIC-20 and stayed with Commodore all the way up to the AMIGA 1200 - then switched to windows 3.1/DOS, and in a job environment supported everything from NT 3.51 (laughed a bit at the previous post that mentioned it) all the way up to now (and Linux - redhat, ubuntu, mint etc.) - and nothing made me want to smash a keyboard like windows 8.

Rob

Use Win7 (64bit)

Most people have it, which is a great advantage if you're looking for help of some kind.

Also, I don't think Windows 8 offers anything valuable and it hasn't been out as long so issues probably remain to be solved by Microsoft. Is the first service pack even out yet?

No real reason not to go with Windows 8, even if only for the longer support period and future hardware compatibility.

I would not go for a new PC with an outdated operating system!
That being said my choice would at the moment be Windows 8.1 Pro which is supposed to get another major update in March, adding even more new functions and improvements than from 8 to 8.1.
The problem is sooner or later the newer software features and drivers will fall behind in development for older Windows versions. It happened from XP to Vista with DX10 for example and with SSD drive functionality from Vista to Windows 7. It does and will happen again with 7 to 8 if you look at DX11.2 now. To take full advantage of your modern hardware, sooner or later you will want to have the continued support of features with your operating system and I do not see this as a given for Windows 7.
On my main gaming rig I switched from Vista Ultimate (64bit) to Windows 8 when it was available dirt cheap. I have yet to come up with compatibility issues on Windows 8.1 which are not caused by missing admin rights granted to the software or missing credentials like .net framework or such. The downside is that some older hardware may not work any longer on Windows 8. My printer for example (granted it is ancient) does no longer work with its scanner, only the printing still works, but I suppose it would have been the same with Windows 7, as the manufacturer ended the driver support with Vista.

If it's only the UI that turns you away from Windows 8, you have various ways to customise it. Ever since they destroyed the Startmenu in Windows 7 (in Vista you could still use the old Windows98-like Startmenu), I never really liked it, so using the new Startmenu of Windows 8.1 feels a lot more comfortable to me now. There are many minor little tweaks in Windows 8.1 (like the new file explorer, the better/faster search or the advanced task manager) compared to Windows 7 that far outweight these design issues if they are not your main problem with Windows 8, like it was for me. One gets used to the design, although I would like to have some more built-in options to customise the Startmenu, like defining the colour of the tiles by yourself. I have the feeling they will add such minor tweaks with Update 1 coming in March though. At least I hope so, even if I can live with the current state.

Windows 7 x64 is your best bet.

Windows 7 x64 (get the Professional version unless the extra cost is a problem) unless:

You are running antique hardware that is 32-bit or does not have signed drivers. For these, use Windows 7 32-bit if you can, or rev-lock to XP SP3 if you must.

You have hardware that actually takes advantage of the DirectX improvements in Windows 8. This means AMD APU and Dual Graphic configurations. These actually run a lot better under Windows 8.1.

The pushback on Windows 8 has been so severe that Microsoft is likely to drop it in favor of Windows 9 and actually listening to their corporate customers before doing anything that grotesquely stupid again.

I cannot say anything about game compatibility, as I still play games on XP (and OpenSuse Linux if it's supported).

Windows 7 64bit is a very stable OS and a look in GoG.com's catalogue shows that is more compatible with games than 8.

Since I have an installation of Windows 8 upgraded to 8.1, I have to admit that as an OS is as stable as 7. If you can accept the always on DRM of using your live account, windows 8 and 8.1 have some interesting features. I don't like to have an always DRM though, so I use an offline account.

Metro interface is inconvenient as it could be and it's 8's greatest fault. If Microsoft bring back the familiar start button and leave Metro as an additional choice, everything will be much better.

Windows 9 are going to be announced soon. So you can just pass 8 and upgrade from 7 to 9 at a later time.

It seems the only clear message is that there is no clear message :P

Win 7 seems to have popular fans and for those already on it little to no real reason to shift to Win 8. Meanwhile those who have shifted to 8 appear to be general fans once they get over the learning curve of using it - whilst at the same time admitting that some things simply don't work on in 8 any more.

Stick with 7, if you don't need many of the features because you simply don't use em find a lite version - it's the best choice if you ask me, until 9 comes - provided it's not a mess...

Windows 7 x64 (Main OS, DirectX 10,11) and Windows XP x86 (For Finicky Games, DirectX 9,8,7 etc)

Ubuntu... No wait that's not windows....
7 is pretty ok imho.