Windows 7 boots much faster than Vista, UAC has now some options between on and off, Windows 7 allows uninstalling IE and media player..... I don't see a reason why anyone would choose vista over windows 7. As for windows 7 vs xp, have a ssd? then moving to windows 7 will be almost mandatory as xp has zero optimizations for them, xp requires a freaking floppy drive to install raid drivers, support for optical sata drives plain out sucks in xp. Performance difference? whats that good for? Even if xp runs faster, all that means is that it waits 0.0003 seconds longer for the user to catch up. Security? currently they are all the same, just don't login as a admin by default and you are pretty much good to go, of course ms is too stupid to figure that out, during win7 install it still only creates one admin accout which is then used by default, however, in the future security will cahnge in favour of the newer ones as ms will certainly not update xp as often anymore.