Prismas are okay, but I'm thinking of switching over more to Faber Castell color pencils and using Derwents mixed in. For me, Derwents and Faber Castells are easier to blend naturally for me, and I oh so hate using that blender pencil as it cheapens the quality of your shading even if you only use a little bit.
Guess it depends how you work with it as to which color pencils are best for you. :x