No question. Stepan is the best option out of all the options you have listed. Berglund definitely has some upside, but it looks like Stepan will have more opportunity to have a better year. If he continues to get 1st PP time, which he should, it will end up being a one-sided comparison. That PP unit is gonna be ridiculous before it's all said and done.
Desharnais is intiguing, but I'd still rather have Stepan.
20 Team $$ Dynasty League (23 man roster, 27 man minor roster) w/Salary Cap at $80M on Fantrax **1 Time Champ
G, A, P, +/-, PP, SHP, Hits, Blocks, Wins, Save%, SV, GAA. *1 goalie starts
C - Couture, Kadri, Anisimov, Dvorak
LW - Marchand, JT Miller, Grabner, Hartman, Duclair
RW - Duchene, Oshie, Silfverberg, J.Williams
D - Ristolainen, S.Jones, Martinez, De Haan, Del Zotto, Chychrun, Carlo
G - Lundqvist, F.Andersen, Raanta
Minors - Meier, Barbashev, Barber, F.Perron, Heinen, Cholowski, T.Motte, Quenneville, Beaudin, Novak, Sissons, V.Dunn, Lauzon, Hogberg