I have been doing a lot of current market research for new systems both tower and laptops. It all depends on what your overall goal is: Max FPS, Portability, Budget.
On Max Frames per Second - desktop wins and ranges in cost depending on monitor upgrade is avg 1,500 bucks to the elite machines for end all gaming 7,500 bucks +
On Portability - laptop wins (I have seen some LAN computer builds, but that is a custom case build done by me and friends for LAN Parties. Hardly never in the consumer market will you see full size components in a portable case.) and ranges in cost depending on size of viewable screen, blueray player, motherboard upgradable, chipset ect avg 1,500 bucks (I stole mine off newegg for 700 bucks I7 with OC) up to 7,000 bucks +
On Budget - For a budget build the Desk Top wins. You can take 2,000 bucks and get close to a 5,000 machine using some old components like the case and not usually the PSU, HD, Monitor and sometimes RAM & PCI Devices depending on "age of the existing machine". If say, you wanted to be in the 1,000 - 1,500 range you can still come out on top going desktop over laptop in terms of raw processing power per dollar spent. Then factor in upgradable future and the laptop is wiped out of the picture compared to a desktop.
References for your enjoyment. Be sure to look at each part in detail, then google the product and see what a place like
http://www.tomshardware.com/ says about it and make an informed buying decision.
Notebooks -
http://www.cyberpowerpc.com/category/notebook/(These are all 3D ready Laptops, bad too the bone I7 chips ect... Not your run of the mill average laptop)
Desktops -
http://www.cyberpowerpc.com/landingpages/intel/i7/?gclid=CJ35itzsmrICFQKf7QodskAA2QHere are some examples for a 700-800 dollor budget build. All prices listed Lowest to Highest (In fairness too notebooks there are a ton on the market for 700-800 bucks but not in terms of raw processing power)
Corsair Case -
http://www.compusa.com/applications/Category/guidedSearch.asp?CatId=32&sel=Mfr%3BMfr_14991155 Socket Motherboard -
http://www.compusa.com/applications/Category/guidedSearch.asp?CatId=13&sel=Detail%3B31_174_68338_683381155 Processor -
http://www.compusa.com/applications/category/guidedSearch.asp?CatId=22&sel=Detail%3B112_174_68338_68338RAM -
http://www.compusa.com/applications/Category/guidedSearch.asp?CatId=10&sel=Detail%3B30_170_12739_12739The rest of the system would be easily put together and you would hit your goal of 700-800 bucks.
Example of two crazy black budget systems (be sure to click on details and see the triple monitors ect... These are total systems) -
http://www.cyberpowerpc.com/cart/showcart.aspx?url=%2fsystem%2fFang_III_-_Black_Mamba&ref=addHope this helps.