Depends on the job, but I find CR2 or CR3 macemen to be my most effective city attackers. I think crossbowmen can be promoted to be competitive, and be better all-rounders, but in my experience for taking a city in the feudal era, it's macemen and trebs/cats.
But really, I should've taken him out when I had Gallic Warriors and he had...uh...nothing that uses metal.