I've actually spent some time roaming Helsinginkatu and there are a few new cafe/bars that seem nice. Most of the places are complete shitholes but there are a few gems in there.
Also
Cafe Tin-tin tango is nice..AND you can do your washing while having a coffee or whatever
they've got a sauna aswell.
PRAHA is good during the day but gets really loud and crowded in the evenings.And thats more for those who like rock music. Same with On the rocks,during the day.They got really comfy chairs upstairs and a pool table.That's where I chill the most...*pool sharks r us*
But as the other guys have mentioned,Helsinki doesn't have that many good cafes where you can just chill.They tend to be bars....suprisingly