Sieges: Are some units better than others?

[jfp3]

Yeah I read the section in the book but didn't see anything telling me that for instance my Heavy Cav actually know how to get off their mounts and scale a ladder (making them pretty good for Sieges right?). Instead I keep having these images of Bullwinkle head-butting a stone wall to little effect. I do however love these moose charges on the battlefield heheh.

Right now I have a siege going for some 4 turns that has a large number of "animals" in the force and I'm thinking it's taking way too long...so I'll be trickling in some local infantry pretty quick to see if it helps.