I wouldn't mind Guentzel away from Crosby.
That said, I think Guentzel is at his best with Crosby. Guentzel can play pretty much anywhere in the top 9 on the LW. He's shown chemistry with Crosby, Malkin and Kessel. I don't think it's going to be a bad idea to put him on the first, second or third line. I just think he's at his best when playing with Crosby, so that's where he should remain.
Personally, in terms of the LW, I'd put Guentzel with Crosby and Hagelin with Malkin. Those seem to be our two best combinations at least on the LW. As far as RW goes, there's a lot more versatility, but I feel like it's a bit similar to LW. Hornqvist, much like Guentzel, can play anywhere in the top 9 on the RW, but I feel like he's at his best when playing with Crosby. That line of Guentzel, Crosby and Hornqvist was arguably our best line in the playoffs last season. That said, Hagelin, Malkin and Hornqvist was also a very productive line during the regular season, so it's tough. Personally, I think Hornqvist should play with Crosby and Guentzel until that line stops producing.
Then there's if Kessel should play on the second or third line. I think it's obvious Kessel prefers to play with Malkin, but the results don't lie and it seems like the Penguins are a much better team when Kessel is on the third line. Personally, I'm fine with it during the regular season, but I think Sullivan will ultimately move Kessel to the third line during the playoffs. Personally, I'd rather just seem him there at the beginning of the season to be honest. I understand it's an 82 game season and the lineup is going to change throughout it, but I feel like it would be good to give Brassard and Kessel time together before the playoffs start, much like Hagelin, Bonino and Kessel had time due to injuries (Which are going to happen) in 2016. So that leaves Sprong to most likely play with Malkin and Hagelin, which I think has the potential to be a very good line.
Rust can play anywhere in the lineup on LW or RW, but chances are he's playing LW on the third line with Brassard and Kessel. I'm not against putting Brassard on the wing, but I feel like Brassard gives us such amazing depth if he's playing center. Let's not forget that Brassard is a 2nd line center on most teams in the NHL. He's a 20-25 goal scorer and 50-60 point player that came from a rough situation in Ottawa that played a very defensive system. He's trying to adjust to a new system and had to basically play injured his entire time here. I think Brassard will have a very productive season.
The fourth line is most likely going to be Cullen, Sheahan and Aston-Reese. Once again, this forward group is super versatile so guys are going to move around, but in my opinion that's as solid of a fourth line as I can remember in recent memory. Cullen is soon to be 42 years old which is why I think the Penguins signed Grant, well for a couple reasons. One to give Simon some competition (I think Grant will make the team over Simon, I don't see them using 14 forwards) and two to give Cullen a rest. Grant is a very good defensive forward and penalty killer that can play all three forward positions. He's basically what you want in a 13th forward and is a good option if Cullen isn't playing well or needs a few games off.