Why did you ask the question if you knew the answer? And should've put it on the fantasy forum. Voynov is in a league ahead of Faulk and he's much better defensively. Ryan Murphy can rival or be better than Voynov offensively though as long as he doesn't have concussion issues. If you want a comparison for this year though then look at Leddy and Orlov who's just been called up.
Additionally Voynov will always be competing with Doughty and JJ for PP time.
IMO, for points? Which was the question....I'd take Faulk in a heart beat.
Voynov is better offensively than Johnson, the cream rises to the top and that shouldn't be a problem with him. Playing the PP with Doughty is only a good thing for his point production. Faulk on the other hand will compete with Murphy who's one of the most talented offensive dmen in the world when it comes to potential and McBain and Pitkanen aren't slouches.
In fantasy hockey, you go with the safe option. Few players can MA Bergeron their way around. Faulk unless he imporves his defensive game isn't gonna be trusted (especially under Maurice) to get the type of minutes you're hoping for. Since Voynov seems to be sound defensively, he's a safe option to stick.
Also if you want another sleeper, go for Brendan Smith who's NHL ready or maybe Stefan Elliot who might make a similar impact to Shattenkirk last year, it can be argued that he's better offensively than Shattenkirk and Shattenkirk wasn't that great defensively last season in Colorado either.