Hello! Having not owned a Gateway in many, many years, I can't say which is better, but I can tell you that having owned an ASUS K52 for the past year and a half, that ASUS is quite reliable, however, be warned if you buy a new model, replacement parts for ASUS are a little up there in price. This K52 has lasted me a year and a half and will last me for many years to come. I love the laptop. It's fast. It's a multiprocessing beast. It's cool compared to many laptops I've had over the years. It has a great screen, easy touch keys, it's quiet (very, very quiet) and I can play decent games on it if the need arises (Batman Arkham Asylum plays flawlessly on it), although she doesn't see much gaming, she's mostly for school and media.
Also, hard to choose between two models without specifics. Do you have model numbers or specifications of the laptops? Will help us determine what you are looking at, and we'll also need to know what your primary use for the technology will be... what will you be doing with the laptop mostly, what needs must it meet?