Amartya :
I would like it to run games for the next 4 years without much of a hitch so tell me based on that what laptop should i choose
Let's bring reality back into the mix.
If you were to run Witcher2 on s $1200 Desktop (+monitor) from 4 years ago you wouldn't be running 1080p with everything on without a hitch.
Today's gaming laptops are plenty potent, but your expectations may be a bit too high for any hardware solution in existance.
(Your choice of words and in particular and Witcher 2 and similar games.)
Even the most expensive gaming laptops ($1500 and higher for single-gpu) are a small step behind their desktop counterparts as they are now similar GPUs, but are underclocked and may use slower RAM to meet the lower power requirements of laptops. Right now, $1200 will play most games with only the rare few requiring you to turn down some settings. 4 years from now, it will still play just fine, it will simply require medium-high settings or so.
You are looking at high-mid-tier gaming laptops with your budget.
Look up MSI, Sager, and white-box versions of those two sporting 670mx or 675mx from boutique retailers like gentechpc, xoticpc, or powernotebooks. (or similar there are lots) The 670mx and 675mx are underclocked versions of the Desktop 660. (although the 675mx actually has 256-bit ram!)
One word of warning
670m and 675m (minus the x) are fermi versions of the desktop 460 192-bit and 560ti respectively. They are fine GPUs, but multiple steps behind the 670mx and 675mx. Sager has a deal right now where they actually give you a 675m (no x) for the price of a 670m (no x again). This isn't such a bad deal for the price for those willing to tweak settings. Note fermi chips do run warmer... but the cooling systems in the laptops we are talking about are more than capable.
FYI the 675m is only about 7 months old. (rebrand of 580m which is 17 months old or so)
The 560Ti it is based on is about 2 years old.
(someone claimed it was 3 years old... it's not)
One other possible lead is the GX60 from MSI. It sports a powerful 7970m (a slightly underclocked desktop 7870) and an A10-4600 AMD Trinity. This is much less CPU, but the second-best GPU available now. Don't go this way if your favorite games are CPU-limited.
If you could some save another $300 ($1500 total) it would put you in the market for a Sager I7+ 7970m or maybe even a white-box MSI 680m.
The 680m is a downclocked desktop GTX 670 with slower RAM, and for the moment the performance king in mobile GPUs.