The two biggest forums on TTG right now are General and Sam & Max, they each have over 40,000 posts. EDIT: Forgot to mention that ToMI is closing in on 35,000 posts already
I decided to calculate their approximate posts per day, and compare to Monkey Island forums:
General: 23 Posts per day
SnM: 32 Posts per day
And Monkey Island??
480 Posts per day.
That is more than every other forum on here put together.
Ridiculous, no competition.