Its not because he is a barrel-chested beefcake - although that doesn't hurt. Its because Halsin is literally the first person you meet who is actually concerned for your well-being AND what we call a well-adjusted person.
This leads to an over-arching complaint about the other companions and that is they all basically just suck as people. Someone started a thread saying that they couldn't see why we were chosen as the party leading given various personalities. And it finally occurred to me that without your leadership every single one of these people would end up dead very quickly.
Gale would find some dangerous magical thing and poke it and end up dead.
Shadowheart would walk off a cliff giving the stink-eye to a porcupine that she thought was staring at her.
Lae-zel would have been eaten by Goblins or hung by the tieflings for being over-aggressive and arrogant.
Wyll - convinced of his own legend would take on the Goblins solo and end up eaten.
Astarion would end up dead trying to drink blood from some rando person or captured by his master or in service to another powerful entity who can protect him.
These aren't adventuring companions, they are people that need a life-assistant or they end up strangling themselves trying to put pants on!
That is when they are not in "disapproval mode" of every single decision you make.
Then you meet Halsin, the first person in the ENTIRE game who is focused on the bigger picture, gives you good advice, shows actual concern for your well-being...and yes he is a giant hunk of man. But its so NICE just to have an honest, respectful conversation with a normal person...who can turn into a bear sometimes. I found myself thinking, I would gladly trade every single one of these idiots to just go off adventuring with Halsin. Like, if someone offered me half of an opened mustard packet for the lot of them I would take the deal.
Like I have already decided, despite anything else Karlach is going with me, because she is already 1000 x better - personality-wise - than any of the other companions. Me, Karlach, Halsin and whoever else....we will have a nice chill adventure and be respectful of each other just crackin'-wise and kickin' butts..