I've had lots of Dells and always been happy with them. I agree not to get it from Best Buy though -- you can probably get a MUCH better deal online. Look for some of the online coupons and deals at sites like
gotapex.com, etc.
I had a Vaio laptop once and was very happy with it -- but Sony support sucks imo... At least it did 5-6 years ago when I needed support from them. Dell support is pretty awesome -- especially if you get the extended warranty that covers everything on your laptop, including spills, drops, etc.
If you have the money, I would definitely buy a Mac! It's going to run you at least $1100 though ... however, I would say that it is completely worth it. I got a Macbook Pro back in November after working (and programming) on PCs for years and I haven't regretted it one bit.
Macs are more stable and easier to use (from a standpoint of installing software, not having to configure drivers, etc.). You can also run VMWare Fusion or Parallels to run Windows (or run Bootcamp and dual-boot into Windows) when you want to run Windows only software like PokerStars (although they are working on a Beta), PokerTracker, HUD, etc.