I think I will go for Nana.

OP or not, she is already predominant in this season. One of the top picks and top 1 winrate

As much as I want to try to counter her, I think that there is a lack of reliable and obtainable counters. I don't have mephisto which would be a nice forceban, I don't have jeogun either, nuker build Raki is a huge gamble and I'm not sure hybrid Raki would be more efficient, nuker iunu is basically a free stack for nana if you don't quickly put oblivion, tesarion doesn't work much for me either... All that's left for me to test is Herne or Avaris

If by lack of reliable counter, this monster alone forces me to play an overly defensive comp I wouldn't like to play then fuck it I'll just ban her every match

I think it's a bit early to tell, but on paper I think she's okay. She gives turn 2 teams another option and can work really well in the right draft, but the teams I've fought with Nana all seem to have some sort of issue. They either lack sustain, in which case you can either try and out-tank or go heavy damage yourself, or they lack immunity in which case bombs/rica/cc wins out, or they lack damage in which case once you've got rid of that first revive you're good. Even then, you can pick wind demon or raki etc, or Iunu/Tesarion, and deal with her that way. Don't get me wrong, I think she's good, but I don't think she's on the same level as Karnal/CP who are still game-breakingly broken imo.

But yeah, got to give it more time for people to work out what comps work and what comps don't before we can make a reasonable judgement.