Cosmetically (ASUS), it's really personal preference
Location of ports (ASUS), the location of some ports on the MSI is inconveniently located on the back, unlike the ASUS which is all on the sides.
Heat dissipation (tie), they both have dual fan back exhaust, although the ASUS unit has all of the back area, where as some area on the back of the MSI is occupied by ports.
Quality (ASUS), well ASUS has a better reputation. But I can not guarantee you will not have any problem. It's just the reality bad units happens regardless on the brands.