As city breaks we have done Venice and Budapest, we really enjoyed both but they were completelt different. I wouldn't rule out Rome. By the way we went to both places at the beginning of November wnd both were warm, Budapest it was shorts and t shirts bizarrly.
ah but conversely Krakow is likely to be rather parky, whereas Rome is likely to be quite pleasant in November..... Never been to Krakow, I know plenty of people who have and thought it was great. Was about to suggest Prague but see he's already been!
Krakow is good. centre has pretty old town and castle. Then there are the Jewish ghettos to visit with a few synagogues. There are salt mines outside the city. You can also go to Auschwitz (we had kids with us so didn't), I would recommend it as a city break and we went at a similar time of year.
We went to Rome in December and the weather was beautiful. Sunny days, not too warm, but perfect for walking about all day. Obviously a bit cooler (and sometimes wet) in the evenings, but all in all it was lovely!
Marrakesh. Took dh for surprise 40th birthday trip (before dc). Was in December so wanted somewhere further South. Lived in Paris at the time so lots of connections, and may be harder from here. But it's not eurozone so, once you're there, cheaper than lots of other places.