Koh-i-noor, most definitely! What I have is just a small set of the woodless, but I love how they blend! Second favorite would be a tie between Prismacolors and plain old Crayola or Rose-Art! Is the larger set of Koh-i-noor that you carry woodless as well?
I have both and I love the Koh-i-noor for blending smoothly. Yet, for color, Prismacolor pencils seem to have a heightened intensity. However, I'm really frustrated by the amount of breaks inside the Prismacolor pencil and you can't sharpen them down they just continually break and snap. The Koh-i-noor, of course, don't have that problem.
Uh, oh, I love my Prismacolor pencils too, but do I have to now try Koh-i-noor?! Okay, maybe one or two here and there to fill in my collection of Prismacolor pencils!