No values, most points are for goals and assists with more points for special teams, but we do get points for hits, shots, pim, faceoffs although minimal
If you're going for broke and going all in for this year, you take Letang and don't look back. Niskanen's gone and Letang is going to eat PP minutes like yummy, chewy, Crosby-flavored candy.
If you're playing it safe and think that you'll keep this pick for 3-4 years, take Nichushkin. He has the outside chance of having a ridiculously good year, depending on how he meshes with Spezza-Hemsky. Nich's got the best long-term outlook of the three.
If you are trying to sabotage your team, and tank for a better draft pick, take Yakupov.
... personally, I'd go with Letang because he's going to have the best opportunity of the three, especially if your league rewards PP points.