Of course it depends on your particular talents. You might be good at individuals, particularly faces. In which case you want to draw the minimum of figures. Alternatively maybe you want lots of individuals. But perspective there can be trickier, and you need to make sure you keep a clear focus in the picture.
Nothing says it has to be a combat piece. In fact I've often thought it's non-combat art for wargames that really draws out the spirit of the army. Soldiers do the same more or less what/whoever they fight for, and you can't see the reason for the fight. Something outside of a combat situation tends to have much more emotional impact.
It's also a good way to show that these are "good" people. Humans, dwarves and high/wood elves fight (to an extent) for their homes, families and survival. That is a marked difference from those races that fight because they like it/their Gods told them/the fat toad told them to go this way. To which is it easier to relate?
My personal suggestion would be one of the basic soldiers. Maybe a young man being given a halberd and marching off to a waiting regiment or have his family clustered by his home in the background (one or the other, don't want to crowd things). If you've been bitten by the TVI bug, you want to focus on the basic soldier. He wins your battles after all!
