I find myself on the forums a lot, so I'd have to say the forums. Only because I do not have time to game or hang out in Ventrilo everyday, so I always make an effort to post at least once a day.
I like to talk to people in vent about stuff anything.
I remember back in the day(Yeah its a long time) when i could go into the Tf2 room with Purple,Dj, etc... and talk about stuff.
And now its just like that.
Unless I forgot or get side-tracked, I will log onto the website at least once a day, and scan the forums. Regardless of whether or not I actually post.
I said forums, because people are a lot of the time away from Vent, and I miss them. IRC would really be my favorite, but hardly anyone uses it. So, therefore, I chose forums.
Vent, especially when doing eGO business! Typing back and forth can be so frustrating. Also easy to misinterpret and think someone is being very serious when they are not.