which laptop to buy

Go with the ASUS, that one is a better laptop. Overall it has the i7-4700HQ which is a much faster and quad core CPU vs the i7-4510U which is clocked lower at 2.0 GHz and is only a dual core. While it looks like the 850M is a newer GPU, the 760M is slightly higher in the hierarchy.
 
What? I have an Asus Laptop, I'm even on it right now. I reset it once a month and I never need to shut it down. I've never had a problem with this laptop and I've had it for 2 years now.

I usually find that while some ASUS laptops are a bit thicker compared to a lot of other brands, they do so for the cooling.
 
MSI notebooks are top notch- I have had three in the last few years ( I upgrade often) and all have performed great and hold up to my abuse. You should take a look at the GS60 (15.6" offerings - or GS70 (17") both are nice slim models
 


both MIS laptops are very costly