Daz 3d would be a safe bet probably. It is relatively easy to learn (the basics at least), and there is a large amount of assets (characters, enviroments, poses, props etc.) avaiable for it.
Here is their official site and some more info:
You must be registered to see the links
There are some base assets that are free, but if you want more, you can either buy them though their store, or check out most Daz assets on this site.