I prefer V-ray. To me it provides the best renderings without going too much into the extremely photo realistic side (but I'm sure that is just because I don't like renderings that are too photorealistic). It is also pretty flexible in what you want it to do.

I think the coffee break plugin is the best

http://wiki.mcneel.com/labs/coffeebreak

I HATE V-ray.....admittedly it is super easy. But that is its problem. Too many renders look the same and sort of "plastic" to me. I like good old flamingo sometimes with the lines rendered and entourage photoshopped- sort of an updated version of LTL/Diller and Scofidio renderings.....

depends on type of rendering you want, vray is an excellent biased renderer and maxwell render is an excellent unbiased light simulator

many others

personally use vray, fast, clean, flexible, ubiquitous

IF you have a badass video card... Vray RT for Rhino is the shizzzzzzzz.

I like Vray and I pretty much only use Sketchup anyways.

Vray can be esy to use but the thing that I like about Vray is the customization of it-- meaning that you can manipulate just about any value the program uses to make calculations.

So, your materials are only as good as your ability to manipulate values.

Wait, does Vray RT offer support for CUDA or OpenCL graphics cards now??

I was under the impression they were still using cpu muscle...
If they do, time to get 2xGeForce GTX 460s....

I had been looking into trying out Octane render, but not learning a new renderer is a big upside. I'd like to stick to doing Maxwell or Vray mostly.

Yesssirreeee.

Vray will eventually be ported to OpenCL in the near future for all versions.

Sketchup will be a little bit behind. I've been beta testing the new Vray for Sketchup... There's some hits and misses... but overall it has improved greatly.

The biggest thing I dislike is that the viewport is now detached from sketchup's viewport... so the exported lines don't always match up.

But there is a new working toon shader that automatically outlines edges.

the brazil renderer by splutterfish is very nice as well --- but one great thing about vray or maxwell is that once you learn it, you can use that knowledge in 3dmax/rhino/sketchup/cinema4d/maya/softimage -- for maxwell, it works with even more modelers --- whereas with brazil, it is pretty much max and rhino --- though if this is not a concern, brazil is well worth the consideration

@Unicorn:

I know their CUDA/OpenCL support has been under development for a while, but what I mean is have they actually released a working version?

As far as I can tell (from the Chaos group website) the latest VrayRT sp1 release is still cpu-based with no support for GPU rendering.