I like Hellmut a lot, but Dhukk, Maus Mage, Hakkorhn, Peydma are certainly also viable options. 

I would think that Hellmut would be a really good addition to your 6-star linup

Hmm that depends. What area are you focusing on atm?

Without knowing I would recommend one of these champions, they all have great value and can help you in different aspects of the game!

Visix, Gala, Lua, Mauseleum Mage, Hellmut, Seeker, Hakkorn and Mordecai.

There are also more great champions in your roster worth investing in, but these would probably be one of my priorities.

Kind regards,

BENZOBOY

I'd Say Dhukk since you're missing a good AoE def down.