I can suggest you to go to Tallinn http://tripity.eu
There is plenty to see and do in Tallinn during the summertime.
From visiting a large variety of meuseums, Churches, Parks, walking around the beautiful Old town of tallinn through the twisted Old cobblestone streets, (would recommend going to the handcraft shops, glass blowing shop etc.)Pirita beach and the yacht club is very nice in the summertime, you can also book a yacht trip which is not that expensive.
Tallinn is much more personel, has history and a beautiful Old Town and is half the price of helsinki.
A must as thats the truth.
Stag groups has been blown up by the press. In my option, yes there is stag groups each weekend they normally come on Thurday and leave on Sunday. But we are talking no more than around 60 people per weekend.
Just dont go to the popular Pubs and cheap bars and you will never see them.
There are so many small bars, restaurants etc in Tallinn you are spoilt for choice.