I don't play Fantasy Hockey, but I'd say Granlund is a safer bet and likely (hopefully) settle somewhere in the 50-60pt range depending on health given the minutes he's likely to receive. (#1C, 1st PP unit time)
Dumba is a pure upside guy. A good chance he likely won't scratch the surface of the numbers he's likely to put up years down the line. He's someone who still will need to prove he's capable of being trusted in most situations or he just won't get the bulk of the minutes Suter, Spurgeon, Brodin, and Scandella will receive. He is also starting on a second PP unit which traditionally doesn't receive anywhere near the minutes the first unit does here. He could easily change all that and force his way into more minutes and the top unit, but that's not a given.
If you want a guy who's likely to be safer but won't likely but up bigger numbers, that's Granlund. If you're looking to swing for the fence, Dumba would be it. Ignoring health.