I have an Asus G75 at the moment, which was the line replaced by the G750 - I personally love it. The thing is built like an absolute tank and has endured a lot of abuse through college, and it's still going strong. Stays very cool for a laptop, has an
excellent screen, the speakers are a bit lacking, but it packs more than enough power for anything I throw at it and is probably one of the most physically solid laptops available right now. I do like MSI - they've made nearly all the motherboards I've owned - but I feel like the Asus is a higher quality unit, and is worth the extra as long as you're willing to put up with the extra bulkines that comes with a large 17" laptop.
That's just my opnion. Take it for what it's worth.
Both are good laptops, and you'll have to judge whether or not you'd rather have a 15" or 17" - that's probably the biggest decision.