Windows 7 By far. Windows 8 is still new so not many games support it, Windows XP is too old so not many new games support it. 64 or 32 bit mainly depends on your system and how powerful it is.
My Computer
At a glance
Windows 7 Professional 64biti7-2670QM CPU @ 2.20GHz, 4 Cores, 8 Logical P...8GB DDR3NVIDIA GeForce GT 525M
Computer Manufacturer/Model Number
Dell Inspiron 15R N5110
OS
Windows 7 Professional 64bit
CPU
i7-2670QM CPU @ 2.20GHz, 4 Cores, 8 Logical Processors
If you're wanting to play the older games (2008 and before), Windows XP is the one to choose. If you're wanting to play both newer & older games, Windows 7 is generally better.
Older games will generally work better with Windows XP. Newer games will generally work better with Windows 7.
My Computer
At a glance
Windows 7 Ultimate 32-BitIntel(R) Core(TM) i7 CPU 920 @ 2.67GHzCorsair DDR3 4GbNvidia Ge-Force GTS250
Computer Manufacturer/Model Number
Custom
OS
Windows 7 Ultimate 32-Bit
CPU
Intel(R) Core(TM) i7 CPU 920 @ 2.67GHz
Motherboard
Gigabyte Technology Co., Ltd. EX58-UD3R
Memory
Corsair DDR3 4Gb
Graphics Card(s)
Nvidia Ge-Force GTS250
Sound Card
High Definition Audio Device
Monitor(s) Displays
Envision 19 inch
Screen Resolution
1280x1024
Hard Drives
2 physical hard drives (4 letter drives) that equal up to 626.3 gigs of space all together. I think both are Maxtors, but primary is a SATA drive, secondary is a SATA, too.
It all depends on the game. I have one, for example, that will not run in Windows 7 or 8 yet will run quite happily in Vista. Another game, which I got free with a sound card in the days of XP (before Vista even came out) still runs OK in Windows 8.
My Computer
At a glance
Windows 8.1 Pro RTM x64Intel Core-i5-3570K 4-core @ 3.4GHz (Ivy Brid...4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2...MSI GeForce GTX770 Gaming OC 2GB
4 x 4GB DDR3-1600 Corsair Vengeance CMZ8GX3M2A1600C9B (16GB)
Graphics Card(s)
MSI GeForce GTX770 Gaming OC 2GB
Sound Card
Realtek High Definition on board solution (ALC 898)
Monitor(s) Displays
ViewSonic VA1912w Widescreen (VGA)
Screen Resolution
1440x900
Hard Drives
OCZ Agility 3 SSD 120GB SATA III x2 (RAID 0)
Samsung HD501LJ 500GB SATA II x2
Hitachi HDS721010CLA332 1TB SATA II
Iomega 1.5TB Ext USB 2.0
WD 2.0TB Ext USB 3.0