We have 5 full days to split between Prague and Vienna. Which city deserves the extra day? Thanks!
Try Linz.
Vienna is grandiose. Prague is more medieval and scenic. Look at pictures on line to decide what you like better. IMHO: each of them deserves at least 3 days.
Could use that extra day to go to Cesky Krumlov.
Ilja is correct; you don't have sufficient time for just Vienna and Prague. As it will take a good 5 hours train time between the two, you really have more like 2 days in each. I would spend 2, one day travel, and 2.
I would give an extra night to Prague. All the monuments in Prague are lite up at night. Not always the case in Vienna.