Well I've got Sten's rep way up to about 85 without him challenging me, except for one minor conversation in camp. Just talked him up and gave him a few paintings. Now I have his personal quest activated.
It's rather pointless though since he just gets wiped out in battles, having no shield, and not the HP and armor of Shale. He's my fourth choice (after the doggie).
I use him as "DPS" only, he wont get attack if your "tank" do his job well (Threathen+Taunt), and there fore dont need much HP, whit a mean two handled axe og sword, he do some nasty damage. (note: That I use all NPC's, never leave camp whit the same party)