I haven’t lived in either city but I’ve visited & spent some time in both.
Nuremberg is cheaper, quieter and feels more cosy, and I’d definitely go back and visit… but if I had to live there or choose between the two, I’d opt for Munich. Munich is bigger, more vibrant, better selection of stores (eg it actually has an Apple Store), and it has the amazing Englischer Garten & Chinesischer Turm. Munich had more of the nightclubs & bars that I liked to go to, Nuremberg felt more sleepy to me. (If you know Australia at all, Nuremberg had an “Adelaide” feel, while Munich is more “Melbourne”.)
Didn’t get to check out the co-working spaces, but I’m guessing you’ll find a bigger tech scene in Munich. If saving money on accommodation is your main concern I’d go for Nuremberg, but if you want to have late night Starbucks coding sessions or go clubbing after a hard day’s work, I’d go Munich.
The two cities are so close that you can daytrip from one to the other very easily by train (I’ve done this), it’s just over an hour each way on the ICE trains. So you can definitely see both cities while you’re there.