When I had a 15 hour stopover in Helsinki I chose Hotel Ava.
Like others have said, it is not in the city centre, however, the tram stop is a 3 minute walk and they come every 10-15 minutes and take you to where ever you want to go in Helsinki.
The room are very basic but clean. The beds were very comfortable and Hotel receptionist, Kati, was extremely helpful and very friendly.
The hotel is quiet and you can have a nice nights sleep there. I would go back again.
You have no recent hotel searches.