The only troopers I've used for Westerners are Arqubusiers, who are rubbish! And dopplesoldiers, who are serious mincing machines and handy bodyguards, well worth the 18pts - I'd never leave home without them, except maybe if I'm going the all-papiste route to get all those lovely bonuses they're so fond of.
For Demons, Sloth are a must. Wrath are ok, they can certainly dish out the damage but they won't survive for long once in combat. Never played a scenario before but I'd imagine they're speed would come in handy there. Gluttony is great if you can support him after he's chowed down on some pillars
With cbt5 and some bonuses he could probably get his 3 hits needed on any small based model which takes them out the game for at least a bit. If you're lucky enough to eat an officer and can protect fat bloke after, the game's in the bag. Gluttony with some sloth nearby can be very annoying for your opponant! (isn't that right Andy? Hee hee) Pride can save him a bit too, luring some upstart hard bloke away from your precious blob.