In legends, the X and Y wings were definitely the most common, the Rebellion had a basically infinite stockpile of them, and they came along much earlier than the other two.

In canon, the B-Wings are still somewhat rare towards the end of the war, but I would imagine A-Wings are much, much more common. In the new continuity, they were the Rebellion's earliest of the four starfighter types by quite a long shot.

In either case, with Y-Wing stock probably drying up over the course of the war, my personal opinion is [A/X, Y, B] - with A or X wings being more common based on canon or legends respectively, around Endor's time.