IBM: 8/10 -- pretty good and quick tech support and rma. systems built well but prone to keyboard flex. love it or leave it thumb stick.
Uniwill: 7/10 -- Rather decently built systems but they happen to be sold through some really crummy resellers. Nice style but not always best quality plastic. Some pretty inovative stuff (see hybrid laptop) but very slow release cycles for new models.
ASUS: 8.5/10 --- fantastic tech support. availability from reliable resellers, really sexy...the high end metal models are built like a tank, more run-of-the-mill popular plastic models (see z71v and z70va) take a bit of a hit in terms of construction (see: FLEX) but nothing horrible. If you have a 'Built on ASUS' sticker on your computer you have something to
Dell -- 5/10 -- there are some really nice high end models (see:XPS) but for the most part they are jsut so-so systems. A great buy for a grandma to check email if she can find one of those $500 coupons. Tech support is a hit or miss (has been a hit for me personally). Low end models prone to explode, mid-range models suffer from serious flex.
Apple: 7/10 -- Decent systems, local stores to go and kick the managers ass if something isn't working right, pretty good tech support. However the prices are a bit high for what you get, one mouse button, and current systems (not historical) tend to overheat and turn orange (after you fry an egg or 2 on it). They revise their models often, but release cycles for new models are insanely long.
HP/Compaq 5/10. The hardware itself is rather pretty good, at least the higher end and business models. The V2000 is probably the best cheapo buy. Tech support is by far the worst known to man. Midrange and main stream models are prone to breakage and all sorts of fun issues.