Innsbruck or Merano for New Years

We liked Merano a lot in the autumn and the food is better than in Austria, IMO. It is a mild climate although I don’t know how cold it gets or snow cover on average. It is very pedestrian friendly.

I was there 2 weeks ago, and obviously not winter, but the town is in a subtropical microclimate. Palm trees in sheltered locations. The town has a connection to Empress Elizabeth AKA Sissy who favored this town for her winter retreat.

Innsbrook is big. Or bigish. 300,000 people in the metro area.

Merano has something like 30 or 40,000 people.

That's probably your primary decision tree driver no? Do you want to be in a small City or a big village?

I'd choose Innsbruck over Bolzano as it's so much easier to get to--either by flying into there or taking the train down from Munich.
There again, I spent the Summer of 1970 there, and I'm very familiar with Tirol. I could see 50 peaks of 10,000' out the window of my bedroom. The Austrian Alps are simply breathtaking in beauty.