Forsberg is viewed higher in most rankings because the concensus is that he comes with a little more certainty (albeit with much less upside). There are a few agencies that have dropped him a bit (5-7 range) and its mostly because they question his vision.
I read somewhere that he's compared to an Erik Cole type of player and I'd have a tough time picking him top 5 if that is accurate. PS - I see much more upside than Erik Cole. For me, he's a step behind Galchenyuk and Grigorenko in terms of skill but because he is a "safe pick", he's probably slightly ahead of Grigorenko at the moment.