The articulateds on my railroad are all MTH Rail King with PS2. I find that an odd number of chuffs per revolution (5) provides a prototypical cadence to the stack talk. I do need to stagger the engine's driver sets though.
By the way, the articulateds are best tracking locomotives on my railroad, and especially through switches. The Cab Forward AC9 has the worst boiler overhang, too much for my railroad, so I am thinking about trading it for a Clinchfield Challenger.