i say windows 7. why? compatible and familiar interface and layout. while win8.1 is the latest and greatest and has a new layout and more behind the scenes tweaks i still prefer windows 7. and there have been issues with win8.1 breaking compatiblity with older programs. do you have a lot of programs from winxp that you like to use? that could be an issue for you upgrading to win8, whereas win7 there should be no problems really. definitly something to consider. but the major thing about win8.1 is the tile interface. a lot of people hate it including me. however if you think you can adjust to the new interface, which isn't that all too hard to do, then by all means win8.1. if you want tried and true go with win7.