What is the right answer?
Wet mergers trigger strong star formation.
It is also true that it feeds gas to the central supermassive Black Holes, but the gas fraction lost to the BH is very modest, there'll be plenty left for star formation.
What basically happens is that the gas in the two systems is slammed together, triggering overdensities and subsequent gravitational collapse.
The galaxies with the highest known star formation rates have a very large fraction of merger or strongly interacting systems; they have disturbed "train wreck" morphology (see e.g. the Lyman Alpha Reference Sample (disclaimer: I am a co-author of the linked paper).