I worked on all major brands many years ago.. Go with Toshiba or Compaq.. They are built the best.. and have the best warranty support available.
Don't worry about the HP-Compaq merger.. nothing will change.. there will always be support for Compaq products, just as there was when Compaq bought DIGITAL. From what I've seen, Compaq notebooks seem to be the best value per $.
I've never looked at Sony though.. and must admit, they're notebooks look awesome. Not sure about performance though.
Good luck with your purchase!
Lachlan