I think that if you ask any Kalmah fan this it's an unfair question, since there are at least two songs that every Kalmah fan absolutely loves, and then other songs that they may love as well.
The obvious two are Heroes to Us and Hades...I mean you just can't go wrong listing either of these two as your favorite songs.
I think that besides those two, though, I'd have to say Swamphell. It is a great song, IMO. It's melodic, catchy, heavy, epic, and has a really good solo. I don't think it compares with legendary songs such as Heroes to Us and Hades, which are definitely my two favorite, but since those are pretty much the most obvious choices, and I can't decide which one I like more, I'm going to say Swamphell.