Actually different brand have the "SAME" stuff inside, so there are no such things as giving you better quality parts over the other
Display card wise, Nvidia chips (Not a card in Laptop) is ALWAYS better than ATi Card (This is a given). But since almost all laptop have intelligent control which will shift your graphic chip to on board CPU chip when the graphic running is low or your system is about to be overheated. It is not much of the different. Both 650M and 8730 are mid range card, they will not have MUCH different. Both Chips are 128 bits, while 650M are 900/900/5000 on 2 GB VRAM , 8730 is only 700/1000/4500 on 2G VRAM. The 650M beats 8730 hands down.
Package wise, ASUS have a better design than Dell, and Asus have a better heat exhausting system than dell, so if you consider running your system for a long time with top setting, GO FOR ASUS, otherwise you will be keep using your warranty on your dell.
Dell however, will give you more value for money. That's really depend on you.
If I were you, go to your vendor and ask for a prototype, try on both keyboard BEFORE making a judgment, you will spend much much more time on the tiny keyboard than doing anything else with your computer, it should be the TOP Priority when you are choosing your Laptop. Unless you want to save for money for a chiropractor in the future.
..... and thank for ur opinion....although i've already bought the asus n56vz it really is a beauty 
http://www.asus.com/Notebooks_Ultrabooks/N56VZ/#overview
