There is a certain intimacy that in Face to Face gaming that you don't get with most Online / Hangout / VTT sessions. It's also easier to see if your players are distracted or fading.
Online offers a much larger pool of players for your group. Our current group consists of players ranging from the east coast of North America to the west coast, from Florida to Canada and in between. Kinda impossible to pull that off Face to Face.
Running sessions online also cuts down on time lost to commuting to the game site. Oh, and you only have to clean up after yourself ;)
Both methods have pros and cons, and in the ideal situation I think I'd prefer face to face. That being said, my ideal gaming group spans 3 times zones and two countries, so I'll take the ideal group over the ideal method in this case :)
Face to Face or Online? Which is it for you?