EDIT: Updated with another version that makes comparing more easy on the eye. (Fixed perspective, gradient color, fixes on the previous blender version)
Well, as you can see, I compared 3 programs I do XNALara renders with, I'll tell you the differences of each IN MY OPINION, so my assumptions might be wrong.3DsMAX: Renders the most realistic lightning and materials (especially when using mental ray), as well as offers the most options to tweak the model in whatever way desired, but a bit hard to cope with/handle.Render quality: High
Ease of use: Low
PC Strength needed: HighBlender Cycles: Free to use and a bit easy once you learn how to set nods, lightning and such. A bit hectic when setting the camera (again, in my opinion) and using nods is a bit of a hard task, especially when you need to assign each and every material. But if you know what you're doing, you got a good 3d program with high quality rendering.Render quality: Medium ~ High
Ease of use: Medium
PC Strength needed: Medium ~ HighKeyShot: One of the easiest 3D programs out there, as well as produces amazing results in several clicks, but a bit narrow when it comes to super tweaking the lightning/materials (unlike 3dsMAX).Render quality: Medium High (If you know what you're doing)
Ease of use: High
PC Strength needed: High
So as you can see, those are only three 3d programs out there, there are many others fit for rendering in high quality, such as, for example, Maya, or Poser.
Experiment to find the one you like best of those, I can't say those are the most popular in either xnalara renders or any other renders, but I can say I've seen these 3 used the most (alongside Daz Studio though)
Furthermore, I'm not a huge 3dsmax pro or a blender cycles pro, but It's a glimpse of the results you can get through them.
I hope this helps you in choosing the best program fit to your needs. Sooo tell me which you like best below, perhaps tell me what you find easier, or what I should explore next.