Here's one viewpoint on colored pencils, which I used to use quite a bit though currently not so much. I strongly prefer Faber Castell Pitt pencils to Primas - although that doesn't help with the cost. The reason is that Prismas have one huge weakness with a number of people. The 'lead' in Primas is spot-glued or spot welded to the wood cylinder in several places over the length of the lead. What this means is that if a Prisma is dropped, or sometimes just when sharpening, one of those attachment points may break. That in turn means that a length of the lead is no longer attached and may literally fall out while you are using it. Or, when you go to sharpen it, the unattached part falls out. This can (and does in my experience) get very annoying. Faber Castell pencils, on the other hand, are bonded the entire length of the lead, so that this is not a problem.
Secondly, Prismas are wax-based and Pitts are oil-based. So if you layer heavily with Prismas, you will get a surface sheen or 'wax bloom' that alters the appearance of the surface. This is not a significant problem with Pitts.
This having been said, lots of people use Prismas with excellent results, so as with any brand there are folks who have the opposite preference.
As to Derwents, I never have used their 'regular' colored pencils. I use their Inktense, Graphitint and regular graphite pencils and find them to be good products but of course the first two are water-soluble so they are a different animal than Prismas or Pitts.