out of these three champs, which one would you say is the most unplayable/broken?
In your opinion of course

Heimer

Karma and Sej are good if in the right hands. Heimer can be as well, but only to a point.

Agree with Veric.

Karma, i've personally wrecked people with heimerdinger (including a 2 hour TT match) and i've seen some amazing sej plays.

Sej: Is actually pretty decent. she has gap closer/dash, stuns and slows. The only reason she falls behind is because she acts much like a combination of shyvana and nautilus. only naut's stuns are much more consistant and shyvana puts out alot more dmg. making sej a less picked champ.

Heimer: His mechanics are somewhat similar to anivia, he has an awkard slow ranged stun and alot of burst. and his ult tied to his turrets might as well be a wall. unfortunately, his turrets are so easy to knock out in late game that he is bet utilized under a map turret so he becomes useless in the offensive unless he is ahead and the player has great use of his stun ability.

Karma: I'm suprised we haven't seen more of her recently. she works crazy good with melee ad casters. she also kinda functions like galio, in that she can play solo caster lane but really builds mostly tanky due to her passive and her supportive nature.

so to wrap this up, the only unviable champ at the moment is nasus and thats only for professional level. he still does well in lower bracket solo queues

I would say Karma, only because I haven't actually seen her used in all my time playing. So it's more down to ignorance and a lack of understanding that I can say that. I've seen Heimerdinger in use and he can be fairly devastating in the proper hands. And, having used Sejuani, I can say without a shadow of a doubt that she is far from unplayable or useless. As Fel said, she's an odd mix of two characters and sadly she doesn't excel like those two in those respects. But she can be a solid team player and can really shift the tide of a fight if her ult is used properly. Her slows make her a great chaser and I always have fun using her.