Yes, for HBM Immortep is the best, of course it depends on your other heroes as well. Ninja is really good in the arena, especially with his skill level up. But for HBM and Raids Immo is the man. Btw Ninja sucks for raiding, sucks a lot i mean. He`s been my first gem roll hero and everytime he goes into battle he just sprints ahead and dies instantly i always have to use my spells just to keep him alive.