I decided to choose Dzeko. It was a close call between him and Fabiano, but Fabiano will be 30 when the new season starts and I don't really trust 30 year old Brazilians who know that this will be their last chance for a fat contract and they won't have to prove anything.
I've seen a lot of both Dzeko and Fabiano and I don't think Fabiano is superior to Dzeko in any aspect of the game. Both are very good with the ball at their feet, both are excellent finishers, both are strong and powerful guys, both score against big teams, just that Dzeko is not even 24 and he can even improve in the future.
Dzeko will be much more expensive, but he can pay back the money in the future. Fabiano can't.