Obvious/unarguable ones for Boston are Bergeron, Marchand and Chara.
I guess Pastrnak is pretty close to that territory now, he's just been a better version of what Seguin was for the Bruins when he was here. Still though, I do think there's an argument for Horton. I already reflect on his play in the playoffs as something I'd consider legendary. He only ever played in 2 playoffs and was an absolutely massive part of getting the Bruins to the Cup Final both times. Doesn't help that Pasta was very disappointing in this most recent run.
I'm pretty torn on Seidenberg vs. Krug but I think ultimately I'd go with Seidenberg. I don't even know how you can compare the two though, they are such different players.
I would never take Rask over Thomas in anything. Even though the games played heavily favors Rask, you can't just ignore Thomas' 2010/11 season.