We are going to be in both towns, as well as TLL, the first week of July. Another FlyerTalker, who has spent much of the past two years working in Helsinki, recommended the Scandia (Hilton) Simonkentta to me. I was able to get a 92 euro rate there, or I could have used 10,000 Hilton points for a free night.
I have not had the same success finding a reasonable hotel in LED. I'm afraid we are really blowing the budget there, at the Grand Hotel Europe Kempinski. I'll be interested to see what responses you get on LED.
In both cases, I chose the hotel both for its comfort and for its central location. We like a well located hotel so that we can walk as much as possible.