I think in the end'll likely be a wash. Parise is undoubtedly a much more mature player right now than Nilsson, that much is obvious. Yet there point totals are nearly identical at the moment. I don't see Parise having as much room to grow as a player. He'll still be valuable, and should be a very good second liner, putting up maybe 50-60 and bringing leadership and 2way play. I see him turning out very Mike York-esque, give or take and likely with a bit more leadership and defense. He could suprise me, but that's my hunch.
Nilsson though is still quite raw, and is getting by a lot more on his natural ability. IIf he refines his game, adds some muscle and hones his ability to utilise his skills, I see him being a better producer. He may or may not ever fulfill that potential, of course. The rest of Parise's game may make up for the difference in points, but it all depends on how the two continue to develop. Only time will tell. There's no clear answer at this time, IMO.