Should I visit Vienna or Berlin?

I’m very excited. I’m meeting my partner in Prague in four weeks, after a three month separation. We want to do a little travelling, as I haven’t seen any of Europe except for Norway.

We’ve decided on either Vienna or Berlin, and the final decision has been left up to me. Your input would be so appreciated!

We’re on a budget and will be staying in hostels. We’re not huge partiers, but will probably want to see some nightlife. Also, I’m a photographer.