Next year yes. But long in the long run I will argue that we need Dzeko more.
Dzeko is a bigger talent and a better player, the likes of him at his age and availability won't come around often.
Krasic is a good player, and will solve some of the problems we have with wide players. I just don't think he has as big a chance l to become a truly great player for us for the next 8 years.
One of my main arguments is that there are not that many world class stikers around, however quite a few wide players.
We have Martinez, Camoranesi, Giovinco, Pepe, Lanzafame. Thats 5 players for 2 spots. I know Giovinco and Camo are on their way out. I would rather give Giovinco another year, and give Camo his last year and see where and how Krasic, Hazard, Navas, Bale, Alexis Sanchez, Elia, Zarate, Leon, Di Maria are doing in a years time.
Adding Krasic will improve our squad, but not sufficiently to win anyways. Out current wingers can get us into CL, and it would be easier to get a good winger next year than a striker of Dzeko's skill.
That is why I think the best long run choice would be Dzeko.