Sure, Vash is cool with his superb gunmanship, otherworldly powers, protecting people, and fighting for love and for peace.
But it's the littlest moments that hit me the hardest.
A line directed at the unborn chicken in the egg cracked while training, that became his breakfast. Such a trivial and small thing for most, but not for Vash. Not too small to notice, not taken for granted. Holy.
Edit: As you can tell by the comments, I've been informed no chicks were harmed in the making of Trigun 98, which I'm delighted to learn, but you still get the point, right? ; )
And in Stampede, for me, it was this moment when I knew this man was worth following him to the ends of the planet through whatever hardships
Held at gunpoint, about to be either killed or turned in to the military police (yes, we know the townspeople's motivations, and no, it's not supposed to be an easy choice), and he gives them this. The gentle look and smile of understanding. Not a hint of "oh no, why me, please no". Instead it's "if it helps you at least a little, I accept this fate".
I'd read a few words about Trigun before getting into it, and caught mentions of something-something religious out of the corner of my eye. Then, watching this scene, I thought "Wow, this must be what they're talking about; this guy is all-forgiving".
This destroys me every time, and yes, tears were shed while writing this.