Initiative. Sounds reasonable.
How about PS? Dengar+VI is an 11 while Whisper is a 9 at best.
Pilot Skill doesn't come into it with Dengar's counter attack. Pilot skill determines the order in which ships move during the Activation phase and attack during the Combat phase, as well as the order in which ships are placed during setup.
Dengar might attack before Whisper during the Combat phase, but when Whisper's attack is over, her ACD and Dengar will trigger at the same time. This becomes a timing conflict between the two players (not the pilots) and the player with initiative resolves their ability first. That is the function of initiative in X-wing - to decide timing conflicts.
I'm pretty sure that the VI+Tactician suggestion was to keep from ever having to deal with which comes first. The stress from Tactician would prevent ACD from doing anything.
Edited by WWHSD