Personally I'm taking Klingberg. I mean, Klingberg is a consitent 65ish pt defenseman. How many of those are there? Ask yourself this - what do you HOPE Dahlin becomes? Probably what Klingberg already is. I love potential but when you have a player that you hope your potential becomes and the age of the player is still young (Klingberg is what, 26?), you take the sure thing.
IMO the odds of Dahlin becoming a 70 point Dman or better than Klingberg are slimmer than him just being really good (50 points plus) or what Kling already is. Just my 2 cents.