From: Kyrah Abattoir
Zbrush & Mudbox, good for high resolution models
bad for sculpts.
Not quite true.
I admit, the higher resolution model doesn't cause a higher resolution sculpt...BUT:
You can opt to sculpt with low-poly meshes, in both programs (Unless I'm mistaken), which is just as useful as any other program's sculpting feature. I know that I personally use Blender's sculpt mode for quite a few things for SL sculpties. It enables symmetrical editing with ease, some people are just plain more comfy 'drawing' their changes, and so on.
Beyond that, you can up the poly count of your model and add tons of details, then use that higher-poly, more detailed model to bake textures, increasing the aesthetic quality of the end product. Faking contours and whatnot with textures by hand is one thing; actually baking real details into a texture then using that on a lower poly object is very different, and very useful for things like SL sculpties. (You've seen the cubes textured like garbage dumpsters, that look relatively nice? It's like that!)
Every texture that I bake uses a higher poly model than the one I export for sculpties, because I have more pixels, and detail, that I can use. Higher poly meshes don't just allow for more detailed textures, but also for smoother ones! If you set an object to use smooth shading, rather than 'individual face' shading, a lower poly model will still have inaccuracies and oddities that a higher poly model can more easily avoid.
I know that ZBrush offers some absolutely awesome texturing abilities, and I assume Mudbox's are somewhere near the same quality.
I don't personally know about Mudbox's primitive capabilities, but ZBrush has some nice options, that allow you to create a basic mesh without too much hassle, and work from there.
Don't knock the high poly sculpting programs, they have their wonderful uses, even in a low-poly world!