You might have more luck if you use the Verithin pencils. Prismacolor pencils are very soft and are known for breaking easily but supposedly these prismas have harder leds that can get to a fine point without breaking so easy. I've never tried them, though. I also use the faber castell Polychromos (on paper, though, not vinyl) and these ones are much harder and hold their point longer, but you have to press harder or layer more to get the same level of pigmentation as with prismas. The pablo Caran d' Aches are also really nice. I believe these are also wax based like the prismas (either these or the luminance, not sure right now) so they have similar levels of pigmentation as well as hardness, though they don't break as often.
Of all the artist quality color pencils I'm pretty sure Prisma has the most color variation and it's the cheapest option (and assuming you live in the US, it's also the most accesible).