very interesting subject since I LOVE BOTH OF THEM but like Kira I'm way bias over DATSYUK's SKILLS !!!
Like many here, I think Zetterberg is overall more rounded but I don't agree that he's more COMPLETE. I think Zetterberg do everything , absolutely good or above average while Datsyuk is ELITE in some aspect & average or a bit below average on other aspects.
The knock on Datsyuk right now is his endurance, the tough schedule of the NHL would make him difficult to stay healthy 100% (at least that what I see in the last 3 years).
The knock on Zetterberg is that he's skilled, but right now except for once in a while, he didn't translate his full talent at the NHL level. Because of that he could become an elite specialist instead of an elite player meaning he's starting to get the reputation of great PK player, good 2nd liner.
I would pick Datsyuk over Zetterberg anyday of the week but I would hate to choose