I gotta say, I hate to break it to you, but Finland wasn't a Viking.
Denmark is where the Vikings originated from, which spread to Norway, and next Sweden. Finland had nothing to do with the Viking raids.
As for raiding, Denmark did most of the successful raids and pillaging. Sweden tried, and didn't succeed much. Norway raided a small bit, and instead focused on exploring. As for Iceland, he wasn't a Viking for too long.
Denmark is where Vikings came from originally, and they did most of the raiding and pillaging. Successfully.
Sweden did raids as well, most not successful (at least for long.)
Norway did a few raids (Mostly on Ireland) and went to explore.