I used All of Vista and XP versions. It means 4 versions.
So.... XP 32 definetly if you want fast OS and better for gaming than Vista.
There are many topics on the internet that say Vista sucks for gaming if you use Super prefetch, but if you disable it then your OS boots very slow and every application you start takes more time.
Of course, if you use at least 2 HD's in Raid, you get vista to good performance (considering you have bunch of ram already).
Vista 64 should be future, but most of applications don't use 64-bit code, so only advantage of 64-bit OS is it can take more memory, but even then you can use 64 XP which is more stable and faster then 64 Vista.
You can try all of this by yourself. I'm using 2 computers, 1 uses raid, 1 not and the one that doesn't use vista speed simply can be called vista slow.
XP 32 bit can accept up to 3.5 Gb of ram, Vista 32 up to 4 I think, but any 64 version has much greater limit.
So, If you have less then 4 Gb stick to 32 XP, otherwise you can try XP or 64 Vista, depending you want nice and fancy-resource-hungry looking vista or great working XP. Vista has some advantages, but for now, still XP.
I switched back to XP and will never come back to Vista...Maybe windows 7 if it gets good optimization.
I must mention, i get blue screen on Vista without reason. Nothing was working, just desktop standing (this was 32-bit Vista).
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