Two Rivers Archers:
Some of the best archers in the game, they combine range and accuracy with high damage output, a deadly combination. They are also relatively cheap and their arrows deal armor piercing damage. The only downside is that if they get stuck in melee they are dead.
Perrin's Wolf Guard:
The Wolf Guard are trained with the Two Rivers Longbow and are the best archers in-game. They out range everyone but the two rivers longbows, and they can do more damage than them. They also are quite capable in melee, being able to stand up to most non elite units.
The winged guards of Mayene are excellent heavy cavalry. They can defeat most other cavalry in battle, and are a very good option for a general's unit. They can also act as guards for the archers, as any unit that can trouble the archers tends to not be able to stand up to the winged guards.