Either Mitch or Lilly. Auston does have some bit-back in his game now and uses his strength to gain leverage on the puck. Tavares and Nylander also routinely use their strength to outmuscle their opponents even if they don't fight or engage in scrums all that often. OEL showed some snarl while on Florida, and Minten is an OHL'er so this comparison is entirely unfair for him right now.
I like Lilly but he gets bullied quite a bit, the Bruins ate him alive. Won't forget the one time he landed a decent hit against some Bruin only to have Marchand and that same Bruin plant him on his ass shortly after on that same shift. I guess he should get points for at least trying and the fact that as a defenseman he's subject to more punishment than forwards, especially wingers who can choose to avoid it, like the next guy I'm going to mention.
Mitch brings little physicality to his game and also refuses to fight back in any situation. The guy looks like a lost child any time a scrum breaks out and he's on the ice. Dude also acts like a piss-baby way too much for someone who wears a letter and his constant fighting with the media is a poor look and not reflective of someone who truly doesn't care what the media thinks.
So Mitch is the softest with Lilly second.