The LG has better color accuracy, it's cheaper (and Best Buy often puts it on sale for $280, I'd watch for that), it has a matte coated screen, and a 3-year warranty with service centers all around the world. LG is the largest producer of LCD panels in the world. That line of LG monitors are currently the fastest panels available.
The Gateway comes with a better stand. However, both are VESA mounting compatible so you can match them up with any after-market stand you like, if you care about the stand. The Gateway also has glossy coating on the screen, which creates a sharper picture, yet also creates a lot of glare if your computer room isn't perfectly dark. From what I've seen, it has poor color accuracy. It has a one-year warranty.
In my opinion, the only advantage of going with the Gateway is that it has more inputs (component and HDMI), so you can hook up a gaming system or DVD player if you like.
edit: The Gateway's energy consumption isn't listed on the site you linked. Gateway's site claims 55W, 10W more than the LG.
