The best to learn is 3dsmax
You can import external 3D models (from web libraries or from poser/DAZ, or Zbrush/mud) or model them yourself.
You can animate easily with the biped.
You can make great renders with the included renderer Mental Ray (used for Riven !).
And there are so many great tools !
Well, when I said 3dsmax is the best, it was a kind of joke, because some prefer Maya, others Cinema4D, it's a matter of feeling... but honestly, if you really really want to make 3D, you have to use one of those.
The trouble is still the price, but you can get the student version for free which will leave a watermark on your pictures. Great to learn and see if you like... Then if you chose to go further, you can buy a full stand alone licence for 4500$
The best free solution is blender of course (quite hard to learn anyways), but this soft is amazing and as complete as the others.
For those who want to model like it was some sculpture by hand, you can try Zbrush or Mudbox....
Else, you need to learn the traditional modeling technique ; just search for tutorials about "box modeling". This is the beginner's way ! Needs hours of training, but it's not that hard. It's more a question of logic.
All I can say is : if you want to make 3D, just be sure you have enough time ! You won't do anything in a few minutes