I'm wondering what the rationale behind this list is? Because few of these make the best of lists. I'll address the ones I've been to.
Cologne: Fine, nice with the location in front of the Dom, but not amazing.
Leipzig: Stopped en route to the much larger, more unique, and famous markets in Dresden. It was nice, but I can't imagine visiting Leipzig and not visiting Dresden.
Nuremberg: OK, I haven't been, but that's only because everyone who has been has warned me seriously not to bother, that it's pretty standard but VERY crowded as one of the most famous ones. If you do go do so early in the week.
Karlsruhe: This one I'm just baffled by to be honest
I'd do some research in this sub and revise the list, and I'd consider linking cities by train instead. My favorites (trying to be unbiased) are Stuttgart, Esslingen, Ludwigsburg, several of the 50+ in Berlin, and Dresden.