from a personal view, i started with DazStudio, and did 99% of my work in that until they brought out DS4, which has a totally alien GUI, plus it is still in a perpetual beta state.

these days i primarily use PoserPro 2012, the render engine is considerably faster, the material room is a lot easier to use ( it has REAL documentation, plus there is plenty of support on the forum here and at rdna for it)

Poser has real IDL (DS can only approximate it with a plug-in( Uberenvironment 2, built in now) ( comparable quality renders would take 2 or 3 times as long to complete in DS)

with Poser you can turn nearly any outfit to dynamic, or easily make your own dynamic cloth to use

DS can only use dynamic cloth made by a third party ( through the Optitex simulation plug-in) atmo, only one 'maker' from Israel who works with a few PA's.

in Poser, SSS is easily applied via either a built-in macro or by a free script (by Snarlygribbly) called EZSkin, with various parameters that can be easily tweaked to taste.

DS has SSS through another plug-in ( Ubersurface) which can easily get broken by a DS4 'update'. no presets available to get a decent skin effect with one click.....

DS4 also installs a Content Management System ( as a Windows Service!!!) that runs ( as default) everytime you boot-up your computer)

Poser has several third party library systems that are excellent for sorting your content as you really want.

Poser has Service Releases that apply bugfixes and updates by incorporating with your Poser install.

with DS you have to download the entire app everytime there is a bugfix etc.

did i mention that Poser still comes with a couple of full manuals, in .pdf format?

DS has no manual, only a bit of online wiki stuff and a few vid tuts on youtube.

Gen 4 ( V4 and M4 etc) still has enormous support in the market.

 DS4 >ignore those who say that you can easily use Gen 4 outfits/hair etc with Genesis/V5.

DS4>the Autofit plug-in barely works ( best on tight fitting stuff, still cannot do shoes/boots very well, at all. destroys all morphs that are in the outfits/hair etc.

DS4 >can be fixed ( to an extent) via the Pro rigging toolset etc. but quite a bit of work entailed ( again, very little diocumentation on how to use the tools)

Poser has good documentation on its Rigging tools, both as .pdf that come with it, and several long ( 45 mins approx) vid tuts available( free)