Halbediers vs. Early Arquebusiers

I've hit a state in my Florence game by 1470 where I control all of northern Italy with "decent control", the largest standing army in Europe, and the highest literacy bar the papacy.

I'm far and away the greatest land power in Europe. I don't raise levies anymore at this point. But I'm still bothered by one question

Who is better halberdiers or Early Arquebusiers

I just got this pile and shot era gun regular but I can't decide if I want to build it or not.

My current army comp is 2 armies, with their formation, below

16 halberdiers (8 left and center) 14 light lancers (2 left and center, 10 right) 14 cannon (reserve) 10 supply (reserve)

My handgonners upgraded into halberdiers. I initially planned to have 2 gun units in the left and center flanks.

What's the benefit of gun units?