The only useful companions I've found are Frostbeards, Healers, Willowbarks, Luckys or Bloodaxes. Frostbeards have the best scouting, Willowbarks and Healers have good healing (I can't really tell their difference except the willowbark will ***** at you for raiding towns and the healer won't), Luckys are by far what i look for and I check the encyclopedia often to see if any more Luckys have been generated since they have 60 tactics which means you can send them off to lead armies and caravans and not worry about them getting thrashed every two seconds. Bloodaxes have 30 tactics (thought it doesn't show up on their character sheet) and usually there's only one Lucky in a playthrough till later so I use them for the same purpose as a Lucky. Anyone with the name, the Red, or the Shieldmaiden is a baller tier combatant but honestly so are upgraded units and you only get limited companion slots so I tend to ignore them maybe only picking up one (in my Battania game I picked up an Aeric the Red cause the name was too perfect). I haven't really found much use for Roguery companions and I really really wish that there was an Engineer companion that I could actually make my engineer but I haven't found one yet.