For desktops I'd say HP, then maybe Dell if I absolutely had to and HP were out of stock.
For servers, HP definitely (particularly for blades and virtualisation workhorses), then Sun's x86 gear which packs a lot for the money... Dell servers are, and always have been, total !!!!e. Perc RAID controllers should be illegal and were probably designed by someone from the data recovery industry.
For laptops I'd go Apple, then Apple, then Apple again, even if you only want to run Windows on it. The rest are little more than also-rans.