i have no idea where the best nightlife in europe is. But ive been to croatia... and its a mix of everything depending on where you go. Its so beautiful and chilled out. But if you venture into the cities/towns like dubrovnik theres some really good electronica/techno clubs and some really quirky cocktail bars in like the old town square... In summer, like you say august, they set up beach parties etc. i dont really know what youre into, you sound like you might be into more clubbing or something... But im 20 and a bunch of us went this year and it was amazing...
Or why not try a city like prague/amsterdam/barcelona... its probably cheaper and youve got more choice. It just might be harder to find what you're looking for....