Had a Toshiba that went on two awesomely crappy deployments and worked very well. On the flip side, know a lot of people who are very happy with Dell. Probably comes down to getting whichever is cheapest and meets your needs.
I'd go with a Toshiba - I don't know people who are happy with their Dell / Alienware, and those that are don't know enough about what a computer can do to be annoyed. Dell puts a LOT of bloatware on their systems.