As an expat now staying in hotels when in Helsinki, I would second the recommendation to not stay near the Messukeskus area.
Stay downtown. Scandic Simonkenttä is very central, new and nice; Marski can be OK but maybe more hit-n-miss and not as central. In the Scandic chain I can also second the Grand Marina, it's interesting and pretty well located; if taking the train to the meeting it's a bit more of a walk.
If cost is not a major issue, then change gears and stay at Hotel Kämp. Best location you could have, and simply the best hotel in Scandinavia. Nuff said.
If you're downtown, you can just take the train or 7A/7B tram to your meetings, see
HKL for maps and
Route Planner for exact directions and timetables.
Sami
P.S. If redeeming hotel points, Scandics are HHonors and Kämp is SPG, and are screaming good deals with 10000 points per night redemption.