I can't say which brand is better, but I will at least provide you with some information. MSI is kinda like a new player in the retail laptop marketplace; similar to Asus. Meaning they didn't start selling laptops under their brandname until somewhat recently. Like maybe 5 years ago? Or something like take. In fact MSI Asus have been ODMs (Original Design Manufacturers) for quite some time. They designed laptops for other brandname long before they started to sell laptops under their own name.
Sager has been selling laptops for a long time. I am pretty sure I heard of them back in the 90's somehow. Maybe I came across an old review of one of their laptops. Sager only sells laptops, they are not a ODM unlike Asus and MSI. Sager mainly use laptops designed by Clevo which is a well respected laptop ODM in their own right. The two basic complaints about Clevo laptop designs that I've read over and over again are:
1. They look bland. Yeah, I guess if you want more curves on your laptop then you should stay away from them.
2. Their laptops feel "plasticky", but they are generally well built. Well, yeah their laptop shells are likely made with high impact plastic. If you're looking for an aluminium shell, then look elsewhere.
Many people seem to praise most of Clevo's ODM laptops because they are well designed and modular.
Soooo.............. which one to choose?
Both have similar base price. For whatever reason, XoticPC is charging less money for CPU upgrades on the Sager compared to MSI. For example, upgrading to the i7-4800MQ will cost you $185 for Sager, but $245 for MSI. Due to Clevo's modular design, you can opt for a more powerful graphics card than the GTX 770m. MSI only offers the GTX 770m. MSI offers 3 LCD screen options, while Sager only have 2 options. As for the outward appearance... Sager's laptop looks like almost any other "generic" laptop. But MSI's laptop has angles.
If it were my choice, I would go with Sager because I prefer it's "bland" look to MSI's angular look. Plus, the Sager has more upgrade options.