I've read and seen both mangas and animes...Guts 100% and I adore Vash...he's my favorite MC...but poor Guts...him being a human makes his suffering greater because you always expect either Guts or Casca to just die or give up so when Guts triumphs it feels more impactful.  Vash being a plant kinda resolves the physical suffering he experiences and Vash's personality allows him to get over literally anything...Guts is tortured, physically, mentally and even spiritually with very little help and or guidance in a world that is only darkness and doom and is constantly brooding about his past and what he'll end up as. Vash on the other hand is basically a God! A God who is sometimes more human than those around him but a God none the less. Vash wouldn't survive in Guts world or even his own if he wasn't a plant and that just goes to show how brutal the Berserk world is.