Even though Haohmaru and Mitsurugi are both the MCs of their respective series, I still think Nakoruru and Nightmare are better picks.
Nakoruru is a strong choice in her own right, and all signs point to her being the one if they did go for SamSho, but I personally just really think Haohmaru has great potential to stand out independently. He's got one of my favorite samurai character designs, he really pops whereas I think many similar series would portray a character like this as kind of a 'default'. Haohmaru shines with personality from his appearance alone, and the lack of samurais in Smash overall mean there's pretty much nobody like him to begin with.
I think SamSho's core dynamics are what excite me the most about it being in Smash. So we're talking the fact that you can be disarmed or drop your weapon, "Rage Mode", that kind of stuff. I think going with the somewhat more straightforward swordsman allows these mechanics to take center stage where it might feel like a bit too much with Nakoruru. Who would already have her whole, yknow, bird thing going on, and stacking these abstract mechanics on top of a puppet character feels overwhelming. And that's the stuff I care about first and foremost, even though Nakoruru would be plenty fun.
SamSho character or not, a character who can be disarmed has become one of my most wanted mechanics because of how cool I thought it was in that game. I toyed with a Bandana Dee concept that plays with the idea of needing to run and grab your spear after throwing it, leaving you with various weaker physical attacks until you can reunite, stuff like that.
