It depends on what you want your computer to do and what you use it for. If you want to have a reliable computer, one that will last and will need little maintenance (and that is easy to use) and cost is not a factor, then I'd go with Apple. Apple products are famously reliable, usually repairable (as much as any computer can be), and you can get AppleCare, with is like an insurance policy, fixing anything that goes wrong with it for free. Also, the Apple stuff holds it's value. Just try to sell a two year old Dell for anything close to what you paid for it. You can also upgrade it without have to take it apart. If cost is a factor, then get a used or refurbished one, available through dealers and even the Apple stores themselves.

I like the Dell computers myself, though the Sony is pretty good as well. If you just want a laptop to surf the net on and do some projects, the Dell Inspiron Duo is very good: nice price, solid case and good keyboard that can take some hard typing and not crunch out on you. If you're looking for like a gaming desktop, Dell has some good ones, but Sony has the better graphics, and you can easily install bigger graphics cards if you need to. No, they don't have the resale value that Macs have, but they also don't have the initial cost and you won't have to figure out how to run Windows on a Dell, it comes with it.