I've stayed in various hotels in Helsinki
Scandic Simonkenttä is a very nice hotel, a good location, very clean and friendly staff but can be expensive.
Scandic Märski - again a very good location, clean, friendly staff but as part of the same chain can be expensive.
Radisson Plaza, is a nice hotel again, my only complaint was that the main doors were locked at a certain time and there was no one on the reception desk so if your card didn't open the doors you were stuck outside!
Seurahuone - this is opposite the railway station so great location. Rooms could do with a bit of renovating but they are clean. Has a nice restaurant on site too but I think it is closed on a Tuesday.
Hotelli Finn

it's great entertainment. Drunks in the lift, plug sockets falling off the wall, and a bath that you have to be a contortionist to get into. A bit cheaper than the other hotels but no where near them in cleanliness.