Ulric: I hate him, in the hands of a good player he is reeeeally strong.
Seraphina: My previous main, and definitely strong. Great tower pusher. Is really fragile though.
Violet: Borderline platinum tier. I mean, she is just generally strong against most things.
Zaar: Not that great after his second freeze disappeared, but that darn invincibility skill is always as annoying.
Nova: Anything that can somehow get close her kills her without fail. Anything that can't is dying. For the most part. Also #SnipesAreReal
Cinder: I don't enjoy cinder personally, but her kit is solid with a lot of damage. The push makes a good cinder able to beat most people both long range and close range, by not allowing a close range fight.
Avalanche: I really like the concept of avalanche, but compared to magmatus there is no reason to pick any other tank unless your team is in desperate need of the freezes. In which case, he is great. Also his hammer has such a huge range it's disgusting I hate it.
Galen: I don't know if he is good as I mostly play characters that will beat him in a 1v1 most of the time. To me he seems rather weak though, and his punchout is very easily interrupted.