Fellhound is the bomb!
Don't over look Fellhound. I got him to rank 6, level 60. I've put him in 3 sets of rank 6 immortal artifacts and he can go half way through the campaign, on nightmare, by himself! I like to build up champions in battle, to see what they can actually do and if they are worth the effort. Fellhound makes it easy. Put the one you want to level up and he can drag their carcus to the end to get the experience. His basic attack is a powerful AoE. He bites and they all get bit. The only draw back is, if you put him with a group, he's going to use his group protection more than his attack. He's a powerhouse and very useful, if you use him right.