As one who never pays for computers but finds them dumped (preferably by businesses because they're usually newer) I have to favour Dell.
Dell's Service Tag (attached to every computer) means you can look up the spec and drivers for a machine instantly. I particularly liked their old Pentium2 and 3 Latitude laptops because they sold well, so spares were abundant. They were strongly built and relatively easy to dismantle and reassemble.
For laughs I like my friends' Apple equipment because it cost them a fortune and most have no idea how to fix issues when they arise -- keeps me in beer.