collar on vulkan is pretty much the same as the collar on the koral, which = good.
my only complaint with the vulkan top is the cut. it's made for fat boys, i think.
i'm slim (5'9" 150lbs) and I feel like I'm wearing a collared shirt by the way the lapels close / fall right near my neck. on the other end of the spectrum, the keiko is built for skinny guys and the lapels meet damn near at the waist.
keiko = shows your boobs a bit.
vulkan = hides your boobs, barely shows your neck.
so, if you like your boobs, or are a bit of an attention whore, keiko is the way to go.
if you're amish, or have moobs with pepperoni nips, then vulkan is the way to go.
vulkan is considerably lighter though. and keiko is a pretty light gi to begin with.
both good gis, both quite durable. keiko pants = much MUCH thicker than vulkan pants.