Laptops (Hardware wise)
Best: Lenovo and ASUS. Sony is great too but the VAIO line is pretty expensive.

Worst: HP/Compaq, Gateway

Desktops
Custom built. No question!

Take on Apple: (Seems to be a pretty standard thing going on in this thread so I thought I'd include mine)
Although I'm not a fan of Apple products they are doing great things for a certain market of individuals. Some people don't want options or "complexity". They just want to use a computer to do things without having to figure things out for themselves. Quite a few people in my own family are this way. Personally it isn't my thing so I'll never own one and I absolutely despise their locked-in policies but I don't see a reason to bash it just because it isn't my taste. I'm more of a Linux oriented individual and I mostly use Windows for gaming. What I dislike most about Apple is a select group of their fanbase however this can be said about the fanbase of any product/company.

Well, from personal experience I have used: Dell, Apple, Sony, HP, Alienware, and Compaq.

From my experiences I would rate the best as: HP

And the worst: Apple

Its odd how experiences of other individuals can switch these two or any two chioices around.

Best = Apple
Worst = Acer or Dell

Anything running windows is shit.
A computer is not for games, go buy a console.

What's so special about Apple?
I installed OS X Leopard on a PC (yes you can do that) and I just don't see the big deal with Macs.

best: self made ( i got an alienware)

worst: dell

Best:  Falcon Northwest

Worst:  Apple or Alienware.

Dell - Dell offers decent support, great bulk pricing, and generally does an excellent job of targeting the low-end market.  My only complaint against Dell is that they uses those little dinky cases that aren't too strong and practically require pulling the whole PC apart to swap memory.

HP - A step up from Dell in quality and price.  HP is pretty much par when it comes to computers.  Not great, not awful, and has something for everyone.

Gateway - I haven't had a Gateway experience in forever so I can't say much on these folks.

Apple - Their hardware is pretty shitty.  In my experience, 3 out of every 4 macs have hardware issues within 1-2 years.  That's based on experience with Mac Book Pros and Mac Minis.  Considering the premium Apple users pay and the limited hardware options available, Apple really has no excuse for this level of unit failure IMO.

Toshiba - If HP is about par then Toshiba is maybe a step above par.  Can't speak for their desktops but they make some very, very nice laptops.

Sony - I've heard mixed things about Sony so I'd probably put them on par HP.

Alienware - Alienware makes Apple's premium look bad.  You get Dell-quality craftsmanship with a very, very expensive logo.

Falcon Northwest - Very expensive but very, very good.  I wouldn't pay for one because computer technology advances so fast, but these guys do great work.

Best: none
Worst: acer

I can't speculate on "worst," so, on with the best:

Best:

Desktop: Acer post 2008

Laptop: Asus

Best: Asus
Worst: Gericom

Best: Asus, I have a nv50 which runs everything smoothly and haven't had any issues with it in two years.

Worst: Don't know, haven't had any bad experiences with PC's breaking down on their own, rather than user error.