Reddit, help my friends and I decide on a city

A group of around 6/7 lads are heading to Sziget in August and will have 3/4 days afterwards to check out another city before jetting back to the UK.

The options are: Prague, Krakow, Berlin, Munich... and Malaga, as a beach is very tempting after a 7 day festival.

What would you recommend? We'd be looking for somewhere very chilled that has a decent nightlife and maybe 1/2 must-do activities to fill time during the day