This one. Most systems in the spec didn’t have the RAM to run aero effectively, and ran like shit. If you had 1-2GB of RAM, it worked fine; just you had less of that RAM available to allocate to the same apps that worked great under XP. If you were lucky enough to have a 64-bit processor, Vista was actually pretty nice, compared to the XP 64-bit edition and the driver nightmare that entailed.