Vista was a perfectly good OS, you people are just too handicapped to keep it maintained and need features that automatically do that for you.
As for Windows 7 I got Home Premium and it works just fine, the only compatibly thing that I see happening in the other versions is some really old x86 programs compatibility which is next to nothing. I'd say go with Home Premium, Microsoft is just trying to sell stuff to people that you can just get for free anyway and less buggy then Microsoft's products.
Also you're an idiot if you're still using XP as your "Main" OS, XP will be out of compatibility with all new things by the end of this year. Not to mention how much stuff doesn't work on it anyway.