I've owned a Toshiba, Sony, and Dell, in that order. The Toshiba blew a motherboard, but it was repaired under warrenty without much hassle, and worked flawlessly after that. The Sony was very nice and never gave me any trouble. The Dell, a 9300 Inspiron, is big. VERY big. TOO big to consider it to be very portable. And the lack of a built-in microphone has turned out to be a problem with my wife chatting to her relatives. (Saves me a big phone bill, though!) I would not recommend Dell if you are going to use their financial service, as they have the WORST customer service I ever experienced.
I suggest looking first for the features you want, make sure you get at least 1 meg of ram so it will run smoothly regardless of the processor, and get an extended warrenty. Almost any major brand should do nicely then, but I personally think next time I will go back to a Sony.