with all due respect to everyone i've been a proud owner of an HP pavilion for more than a year and all i can say is that i'm a very happy customer! i ordered it online and chose my own specification for it, pretty neat as you can get exactly what you want!
to be honest, i dont think there's any radical change between brands since they all use the same being intel/AMD - NVIDIA/ATI and so on.. the main thing is you deciding where do you want to go with the laptop. do you want to play games? then go for a 1GB card, want huge space? you can always buy external HDD they're cheaper!! the main purchase criteria for me would be the price/value ratio, simply what are you getting for what you're paying for, and for that HP and Toshiba are still the best! if you wanna just listen to every little complain about a certain brand then you'll end up buying NOTHING coz simply you'll always find non-happy customers for any brand. Just make sure to get good warranty (3 years area widely available) and then you'll be somehow on the safe side.
as for MAC, the debate is endless, but if most of you're applications are windows based it will be ridiculous to buy a 3x the price for a machine that's currently running on the same hardware! (hail intel!) unless you wanna go fancy and impress the chicks.. then MAC IT IS!

my recommendation is either try to build it at your own specifications or just check online reviews before buying any model. for sure some models can turn out to be faulty by manufacturer and this is easily spotted with some googling!
good luck!