It depends on what you plan to create. If you plan to learn how to make props, I would go with Poser as Daz Studio ( any version ) is very limited to what you can create prop wise. The same with full custom characters such as monsters for example.

If you just want to create renders, or animations, Then I say Daz Studio all the way. I will say that I am not a fan of D|S 4, as I find the User Interface very cumbersome, and as was mentioned the content management is very lacking. I have been using D|S for close to 6 years now and still prefer it over Poser ( which I do not use or have anymore ).

Then there's the hit on your wallet. D|S 4 Standard is a very solid and functional software, and it's free. If you opt for D|S 4 Advanced or Pro ( my g/f just bought me the Pro version, and I have to say it is growing on me, and it's much better for those of us who are vendors ) you get some cool features, but still have to pay extra for many of the add-ons/plug-ins.

It's really a personal choice. If you are just starting out I would go with the free version of D|S 4, and get some of the older figures and some clothing to go along with it. With the exception of buying a few base models there are many sites that offer free characters, poses, and props. Again as mentioned, almost any content will work in either. The Genesis Model is the only one that's Daz Studio specific.