Donato's upside is higher, Forsbacka-Karlsson is more safer. The Bergeron comparison is a bit of ridiculous right now, besides they both were drafted in 45 and win a lot of faceoffs, nothing similar. In terms of style, Forsbacka-Karlsson is more Krejci than Bergeron. Somehow he could end up a poor man Derek Stepan, 40-45 pts 2nd line C with terrific defense I think I will be very happy. Donato is the forgotten one here, but in terms of hands, not a single one in the system is better than him. While he is good defensively too. But he won't be a C, more of a LW. Forsbacka-Karlsson can step in next season, while Donato may need two more years. But the reward may be much more.
It all depends what Sakic and his team think about. If he think you have too much C, Jost, and Hischier or Patrick on the way, than maybe Donato. If they wanna the safer one, then Forsbacka-Karlsson. As someone who followed them a lot past 2 years, if you ask me which hurts most. I will tell you, both. Maybe Donato since he called himself a proud Bruins prospect in his twitter