I always go with 2 type of archer :
2 proper archer, with low melee stat, but very high range stat, and the poleaxe. Other very important stat : initiative. With low armor
Fast adaptation, Bulleseyes, Bow Mastery, (I also use axe mastery), footwork, berserk, Nimble, fearsome are a must. After that, do what you prefer/most adapted to you Battle brother.
I use them against week ennemy or ennemy with range mostly, or when there is a must kill target (like orc berserker). Just to clean a little the board.
If you are against strong well plated ennemy or undead, put them in reserve.
2 crossbow, with good melee and range stat, poleweapon and heavy armor. Other important stat : fatigue and hitpoint.
(crippling strike), bulleseyes, steel bro, Brawny, backstabber, Xbow mastery, Polearm mastery, (footwork), battleforged. (and whatever you want for the last skills).
I use them as archer and 2nd line, able to stand a fight. I’m still not sure about foorwork, and crippling strike is mostly because I use executionner on some of my mercenary, also useful to reduce effectivness of your opponent early during the battle. When the ennemy is at close combat, I switch to polearm. I use them against every type of ennemy, even undead. They could be one exception : goblins.