Staal I think has the edge...
The points don't look really great at the moment, but I think it's going to pick up soon with their 2nd half schedule (home favoured), plus he is the number 1 guy in Carolina, everything essentially runs through him so it's just a matter of time before he picks up. On-ice SH% of just 5.42 which is very low (PDO: 946). 9.01, 12.78, 8.35 during the last 3 years... His real edge is in SOG, where he averages 3 per game...
Spez is probably right where he should be. At the end of the day he'll always play 3rd fiddle to Benn and Seguin, those guys are clearly running the offensive ship in Dallas. You might get a few more points with Spez over Staal, but I think the lack of SOG (2.15) probably hurts him a bit.
I own Stepan in my league, but other than points, he's not really a great across-the-board option. He does get a lot of time on a pretty high octane PP unit of Nash/MSL/Brassard/Boyle, which should continue to see him near the point-per-game pace. Once again 2.10 SOG/game is nothing special.
I think all of them are all pretty decent choices, you're essentially going to get a player around the 0.8 to point-per-game type of player, decent PPP production, +/- is always a toss up, and hits are going to be roughly the same... Staal gives you a bit more of an edge in SOG, but probably a little bit more of a risk in points too.
Staal for me, but very close between the three.
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Franson is more valuable if HITs and BS were involved... give your set of D, I wouldn't take Franson over any of them.