I would recommend the n15, especially if you're primarily worried about online gaming. You're not going to see any performance improvements in-game as your Internet connection is going to be slower than either card's maximum throughput. You might see some improvements elsewhere, but honestly you'd probably never notice the difference, except being short $25 dollars.
Here's a little more info on it: http://compnetworking.about.com/od/wirelessfaqs/f/5ghz-gear.htm