I usually use combat 1+ medic for scouts, and woodsman I and 2 for warriors.
It's map dependent obviously, since some maps have more hills than forests.
Somehow, it's also strategy dependent.
For instance, if you're not researching military techs (BW or HA) early, you may need your warriors to be able to withstand combat vs barb archers.
Cover is then more valuable than other promotions.