I think the Islanders will be better than the Flyers because Philly finished the season okay, but not great, and they lost Mason, and they lost Schenn, and they lost Bellemare. Sure, the Islanders lost Hamonic and Strome, but they got Eberle, and will be getting some prospects in the lineup. The Flyers have a good prospect group, but Pulock, Barzal, Ho-Sang, and Dal-Colle seems better than Rubtsov, Patrick, and Morin. Patrick is a great add for Philly, but isn't ready to be a superstar player yet. Philadelphia lost their starting goalie, so they don't really have a starter, and their defence isn't great. Their forward group isn't deep enough either. The Flyers have some good prospects, but we're talking about right now, not in 5 years. Some would say the Islanders have JT and that's about it for top 6 forwards, but Eberle could get 60+ points on a line with Tavares, Nelson is a top 6 forward who could get 50+ points, Barzal could be a pretty good player who cod get 50+ points right away, Beauvillier might be ready to take the next step and get 45-ish points in 2017-18, Anders Lee had a great season, i expect that to continue, Ho-Sang could get a 45-ish point season, Ladd should have a better year, and then yes, John Tavares should get 70+ points, also there's still a tiny chance of the Isles getting Duchene. Bailey had a good year too, Cizikas can add some scoring, and overall, their forward group is actually not that bad.
The Islanders coaching change, i think, is a big reason why they came so close to the playoffs. All they seemed to need was a coaching change, and there's a reason why they struggled with Jack Capuano as coach but suddenly started playing better with Doug Weight as the coach. Often if a team finishes the season good but misses the playoffs after a bad start, the next season they miss the playoffs again, but it's not like the Islanders just randomly started playing better and it just happened to be after the coaching change, that's the reason they played better at the end of the season, the coaching change.
The Flyers have a better #1 D-Man than the Islanders do, but Pulock, Hickey, Leddy, Boychuk, and De-Haan is better than Provorov, Ghostisbehere, and Gudas. Sure, Manning can help out on the 3rd pair, and MacDonald's a good player, but the main 3 guys on the Flyers' defence are Provorov, Ghostisbehere, and Gudas.
I think Pulock is a very underrated prospect by some people. He should quickly turn into a #1 defenseman.
Also, when Elliott's at his best, he's a great goalie, but when he's not, he struggles. Greiss is not a guy who seems like a cup winning type goalie, but he could bring them to the playoffs.
So this is why i think the Islanders will be better than the Flyers.