Minga, Oida….!
Lived in Munich for a long time up until a year and a half ago.
Munich city is bigger than Nürnberg.
Nürnberg city walls are nice and the centre has a medieval feel to it and it doesn’t really take much more than a day to explore. Munich, in the other hand, is larger and its buildings generally on a much grander scale.
Both cities have nice beer gardens, yet Nürnberger beer is more varied.
Biergarten in Englisch Garten, Waldwirtschaft (WaWi) if you fancy a stroll south along the river (my recommendation, good Weißbier there, too, not so keen on the Helles they have) or Augustiner on Arnulf Str if you’re in town.
If the weather is shitty there are lots of museums in München to keep you entertained, or just go to Augustinerkeller on Kaufingerstr and drink Augustiner.
Nürnberg has the Albrecht Dürer Museum and obviously the (former) Reichspartiegeländer which is interesting but not sure if there’s enough to do for a whole day.
Nürnberg’s surrounding countryside is pretty, but not sure how accessible it is with public transport.
However, a 35-45 min train ride south of Munich gets you to Tegernsee or Schliersee which gives you those quintessential German stereotypes of mountains, beer and Lederhosen. Bräustüberl am Tegernsee is a nice place to sit on a sunny day with a few nice easy walks conveniently ending there.
A day trip to Nürnberg makes more sense than a day trip to Munich.