They have either higher recon, attack or defence. High recon is compensated by lower a/d and the other way around.I've just bought AHD after deciding to get back into Victoria 2 a bit, and I think I'm going to do a USA 1861 game. I have one question though: What kind of units should I be recruiting for different uses? What is the difference between the different cavalry types?
Difference is not very apparent, so I don't bother thinking about different uses. The amount of cav in effective army build is in any case very low (~2).
Engineers are almost completely worthless. Don't bother. Just Xinf/Xart+2cav with extra inf or two. Then guards instead of inf when you can get and afford them.
Good use of generals and terrain is important. Also getting local superiority. Defend preference instead of attack. Exact composition of forces is less important.