Florida is a much better hockey team than the Islanders. The Islanders are basically the definition of mediocre. They'd be nowhere near the playoff picture without Sorokin. Florida at least has more high-end talent to worry about like Tkachuk, Barkov and Ekblad plus better complementary dudes like Verhaeghe, Reinhart, Bennett (currently injured). Much better than Horvat, Lee, Bailey, Nelson and the rest (even add Barzal if he plays). The Panthers also can score like an elite team, are 2nd in the league in 5x5 xGF/60 which could be problematic. The Panthers are a bit loose defensively but so are the Islanders. I'd worry a bit about Florida's ability to put the puck in the net. They did score 15 goals in 4 games against the Bruins this year.
The only area where the Islanders are better than the Panthers is in net. The Isles have Sorokin who, and don't tell Jack, is a legitimate Vezina candidate. Florida is currently rolling with Alex Lyon in net, a 30-year old AHL journeyman who prior to a month or two ago had 24 total NHL appearances over 4 years.
Ultimately the Bruins should be able to beat either team. I don't really care but I think I'd take the Isles if I had a choice. 'm not really worried about the heavy stuff, they are a bit better suited to handle it now with the additions of Orlov and Hathaway. And Florida has dinks too, and perhaps the baddest of them all in Matthew Tkachuk.