Alright then, let's try it album by album.
Fright Night: Fire Dance
By the way, as bland as this album might be, I still like the youthful energy and will for making in it. After all, it was hard to pick up the worst song: there are no bad ones! Not that there are any very good ones either...
Twilight Time: Hills Have Eyes
Never liked that song.
Dreamspace: Thin Ice
The Worst of All Stratovarius.
Try to beat that someday! Don't.
Fourth Dimension: 030366
I seriously thought of going with Lord of the Waisteland, but I dunno... 030366 ain't that bad even, it has its own creepy personality. Still it IS the worst of the album though.
Episode: Will the Sun Rise?
Basic, nothing special. But mind you, there are no bad songs on this album.
Visions: Legions
No bad songs here, either. Had to big one. This one is catchy but a little over-the-top appreciation for the fans.
Destiny: Years Go By
Never actually thought about the worst song here; that is, haven't found the weakest link ever. Years Go By is as good as any other album track, but as a separate song it feels such a filler cry the most.
Infinite: A Million Light Years Away
Once again no bad songs, but I've heard this very commercial feeling piece too much so that it rather bores me nowadays.
Elements, Pt. 1: A Drop in the Ocean
At this point, the-last-song-always-has-to-be-the-ballad arrangement began boring me already.
Elements, Pt. 2: I Walk to My Own Song
Maybe the first album since Elements that also has some uninteresting material in it. I don't like the latter half of the album that much, sans Liberty, one of the best songs there are. Almost went with Dreamweaver, a song that's never opened to me, but then I remembered IWtMOS. A rather embarrassing and ridiculous song.
Stratovarius: Gypsy in Me
A basic song, nothing very interesting going on. A solid album all the way, hard to find those weak links, although they are there.
Polaris: When Mountains Fall
See Elements, Pt. 1.