I generally take 10-20 vaegir marksmen, a similar amount of nord huscarls, and send in a bunch of mercenaries in the top tiers as cannon fodder since they're such low value for money. Also, I have a bunch of rhodok and swadian sharpshooters as better cannon fodder and garrison troops, and I can get shedloads of them easily.
I do, however, have a bunch of forest bandits as recued prisoners from prior sieges. They're sod all use on the field, so I'm thinking of sending them in early to get whacked.