I personally think John Gibson was the most underrated Ducks prospect... it might be different now, after his WJC success.
I'd say William Karlsson's another Ducks prospect who's pretty underrated.
That's how I feel about Ouellet, he may go from one of the Wing's underrated prospects to our most overrated pretty quickly.
For now I think the underrated prospect(s) are either Landon Ferraro, Tomas Tatar or Mattias Backman. All are underrated for different reasons, Tatar more so among our own fanbase, Ferraro because he sucked the past 3 years but is finally putting it together & Backman because he has solid top 4 potential and some Red Wing fans don't even acknowledge him.
For the Pens it might be Beau Bennett, had two years at Denver which were interrupted by injury (especially his 2nd year) but is leading a rather mediocre WBS team in scoring (23 pts in 28 games) and is 9th in the league in rookie scoring (might be top 5 in rookie PPG),