Depends on what I was doing with it but I tend to buy my prebuilds from a local shop that has always done great by me.

I have owned:

Dell (suck)
Emachine (better than I though but still not great)
IBM (rockin laptops won't buy any other)
Toshiba (laptop..sucked and destroyed after a year)
Sony (it was free and sucked...don't buy the name)
Compaq (can you really get lower than Dell or is it just perception?)