I have no preference in a match-up in the first round, ultimately you have to win 4 series to hoist the Cup, and only one team each year does that. With the Rangers added forward depth, I think they have a chance to beat any team, though don't think there's any team I'd put them clear favorites over.
Of the three potential match-ups (four if you include Toronto) each have strengths and weaknesses.
Penguins - Aging core, but have proven to be resilient and you can never count them out in a game. Great coaching, getting a pretty good year out of Crosby and Letang, Jarry has had stretches of being very good, and they're certainly above average in their own zone. They're near the end of their window, so think they're beatable, but could easily beat you in a series too.
Lightning - Two time champs, who aren't perhaps as deep as they have been in the last two seasons, but certainly have a lot of experience winning. Similar in some ways to the Rangers, and are very comfortable playing tight games and capitalizing on your mistakes, but aren't necessarily as dominating as they have been in recent years
Bruins - Also reaching the end of their window, and with a promising netminder. Not sure whether Boston has the depth this year, but they can be aggressive on the forecheck, and don't shy away from the physical game. Not my favorite matchup with the Rangers, but they're not unbeatable either. Will be interesting to see how Swayman does.
Maple Leafs - When this team commits to defense, they really can be tough to play against, and they transition quickly. Their instincts are still to score though, and that I think remains the bit question there. If they play a sound game in their own zone, then I think they get out of the first round and perhaps beyond....but that could be said about many of the teams, including the Rangers, and I think is one reason why Carolina will be a hard out for whoever matches up with them.