This is where people make a big mistake. Just because Zibanejad is younger doesn't have any bearing on who is the better player now (also he's only 2 years behind Silfverberg not 3). I'm sure there were a ton of 20 year old players in the league when Alfredsson broke in at 23 that had put together pretty nice years...does that mean they had better careers? No...development is not linear. Silfverberg has shown that he has the capability to get better every year he plays and be a completely dominant player. At times this year you could see that. Obviously Zibanejad has shown great potential as well, but not as consistently and he's never been as dominant.
I'm not saying that Silfverberg was miles better this year or anything like that, because he wasn't. He looked tired, and he obviously was having some issues adjusting to the North American game (especially the NHL) but he was noticeably better than Zibanejad when taking his entire year into account. If you add in the AHL it becomes a much wider margin.
I like them both. I think they're both important pieces for us moving forward. I fully believe that Silfverberg will be the better player with the better career.
Silfverberg seems a bit underrated in this thread, and I understand the point you're trying to make. I think the difference between the two is that Silf is really a safe bet to pot 20 goals and 40-50 points down the road whereas with Zibby it's a bit harder to predict what player he'll be. He can be a grinder, 3rd center that provides excellent tertiary scoring, a solid 2nd center ala Mike Fisher or better, maybe even a 1st line center.
With Silf you know what you're getting as far as his low end potential. We just have to wait and see if he can reach 30 goal 60 point territory.
Now with Zibby it's a different story. Like I said he's more of a mystery, and maybe it's the mystery of not necessarily knowing what he may become that makes people think he'll end up a better player. Another thing with him, and this is the most important part, is the big time tools he has. He's a strong skater, isn't scared to skate and carry the puck in the middle of the ice, is willing to lay the body around, and then there's his shot. Zibby's shot isn't the same as Silfv's but it can be argued that it's better(not saying it is, just playing devil's advocate a bit here). He has a heavier shot that's more likely to bounce off the goalie and create rebounds and he seems to be able to release it with a bit more ease than Silf because he does those classic wrist shots where you pull it back and have more space as opposed to Silf who has more of a snapper that's harder to release in traffic. Also, Zibby has a hell of a one-timer. I saw it at the WJC, in the pre-season game vs. Boston when he scored the OT winner, and a few times this season where he scored at least once off a wicked one-timer. That's something that can really help him down the line to score some goals. I don't think I've ever seen Silf release a one timer. Usually he stops the puck and uses his lightning quick release instead.
All in all I'd say the difference between them is that with Zibby, he has so many tools, is younger and is just more of a mystery that you don't know what he'll become and there's so many possibilites. Power forward, sniper, playmaker... He has to find out his game unless he becomes some kind of super hybrid. Whereas with Silf, like I said, he's a safe bet to become a two way 20 goal 40-50 point forward. So you know what you can get from him for sure, but that's his low end potential IMO and we'd have to wait and see if he can further develop his game(learn to get his shot off better, stick handle through traffic a bit more to use his shot and create space, etc.) and become more of a prolific goal scorer.