Great question! I think the best way to promote an app is with a well-rounded campaign that combines a variety of marketing channels and tactics. That way, every piece of the puzzle works together to get more visibility and better results than any one could alone.

That said, there are some channels that tend to work better, especially if you're starting out. Facebook advertising is great because it's self-serve and you can target your ads. There are many mobile ad networks depending on your budget and goals - AdMob, Millennial Media, RevMob, TapJoy, ChartBoost for games - I think the most important thing is to target your ads as much as you can and carefully test / measure.

Would be glad to explain more on a call - there are lots of great ways to promote your app.