Which one is better! HP Pavilion dv6t OR Dell XPS 15

Dear Guys, I'm about to buy one of thses laptops but really need your advice.
Its like Graphics Card Vs Memory and Space!!
Both have the same processors Intel Core i5-460M,
HP offers 6GB DDR3/ 750GB HDD with intel graphics
BUT
Dell offers 4GB DDR3/ 500GB HDD with 1GB Nvidia GeForce with Optimus & Bluetooth
These both machines are offered for $799.
Which one should I buy, Please help!!