I think the big difference is whether you're interested in still pictures or animations.

If you're into doing artwork as in the galleries here, then Daz Studio is definitely better than Poser Artist. The rendering engine can do a lot more, the IK for posing is more sophisticated, and there are fewer quirks generally. The interface is a lot more "normal" looking. Poser tends to hide everything in the interests of neatness. Then there's the proper browser window, rather than Poser's slow, lurching library tabs.

But if you want to make animated movies, Poser is still the best choice. With its dopesheet and animation graph, you can fine-tune animations way better than in DS. It's essential if you want to do more than simple pose-to-pose work. Why they added BVH import to DS when you can't clean the files up is a bit of a mystery.  With Poser you can also rotoscope stuff off a background video, change the speed of an animation, smooth out jagged movements, etc.

I suppose a good compromise is to animate your stuff in Poser, then render in DS! I suspect this is what a lot of people will be doing.