I'm not saying that I've seen enough games (of anyone) to make an expert statement on anything, but Laine and Puljujärvi on the same line seems like a needless overlap. Yes, that line generates offense, but more thanks to the individuals than great chemistry. Laine holds on to the puck a lot and makes selfish, straightforward plays (deservedly so as he has the rare talent of actually getting the puck into the net), which doesn't leave much room for Puljujärvi to use his strengths other than his passing, which, while superb, is far from his only asset. To my logic, it would be more fitting to balance these snipers over two lines, providing both with a more playmaker-type linemate and thus creating two really dangerous scoring lines.
Why wouldn't you put Aho on the same line with Puljujärvi? They have played together a lot, the duo worked brilliantly at last year's U20 tournament (Jesse's 10 posts could just as easily have been 10 goals), and the types just match based on what I've seen. Almost everyone seems to sell Aho a bit short here. I really don't care if Kapanen is older, bigger and the higher-drafted player: Aho most definitely shouldn't be a third-liner.
As for Laine's linemates, Rantanen would be a good fit with his playmaking abilities. Also, this would provide the opportunity for Laine to be a RW once again, as Rantanen can (and according to some opinions, SHOULD) play center. Then again, Laine hasn't shown any difficulties producing offense from the LW position.
So, with these thoughts in mind, my suggestion for the top two offensive lines:
Aho-Saarela-Puljujärvi
Laine-Nättinen-Rantanen
(Should Rantanen move to center and allow Laine to assume the natural RW position, the second line could be Kapanen-Rantanen-Laine, but then we would probably have an even bigger overlap problem with Kapanen and Laine on the same line hogging pucks and trying to be the hero.)