Try starting by searching for ACA, ADT, Revit and you should pull up a slew of other threads where this subject has been beaten to death.
What do you think the future holds? (great disscussion)
ACA vs. Revit #1
ACA or REVIT #2
ACA or Revit
Is anyone tired of ACA and Revit? (my personal favorite)
I'm sure others are in here, I just didn't go through all 5 pages the search turned up and stopped at the second page. Since this seems to be a popular question to ask I figured I would stick this into the FAQ portion of the community.