There are so many renderes on the market that I am finding it really hard to narrow down the list.
I am interested in best render for product stills (no animation) that produces best photorealistic images esp. of metals and gemstones. Any recommendations?
changed category to rendering for optimal responses.
-Willen
My vote is for Brazil. Here is an image rendered in Brazil the center stone is not faceted because I did not want to take the time to draw it. This is a design for a high karat ring and the rendering shows that its high karat.
All my best … Danny
I guess I better put in a plug for my favorite (at the moment!) Octane.
Keyshot
More of that boat render. I’ve got Keyshot and prefer Octane over it. I did some comparisons between the two using the same model and they can produce very similar results but I found Octane much faster. Scenes are quick to set up with Keyshot though.
Well I currently use Brazil! Which I love, the motorcycle below was done in that. But I’ve used Keyshot as well, which is also quite amazing. Just a bit more expensive and not usable inside Rhino. The ship below was rendered in Keyshot.
I was still working out lighting and depth of field on the motorcycle.
Nice!
I would go for Blender - free, much better tools for editing and manipulating geometry and texture mapping than any other rendering plugin. There is an ongoing project to integrate Sycles in Rhino.I’m stuck with Flamingo Nxt with which I am familiar. I’ve attached a Flamingo rendering of a 30’ electric launch. 
I’m a Vray fan, here’s a little test piece I made to experiment with some textures for metal shaders:
Right know I work for Chaos Group, but some time ago I was in the same situation that you are right now. I had around 5 different rendering engine in front of me and I have to decide which one meet my needs. After couple week testing the software I picked V-Ray. The GI quality, AA, speed, support, light type supported and the Rhino integration make my decision easy. So, I picked V-Ray . Of course, I’m working for Chaos Group right now, but V-Ray still my main rendering engine for my personal works.
If you want to lean V-Ray, I can give you a free hour online training.
Like Fernando I tried many different rendering engine and, at the end, I choose V-Ray. Like no other it’s a Swiss army knife. You can use it in so many different way getting from fast rendering to pure artistic images.
The v2 for Rhino isn’t perfect but absolutely stable,never crash. Chaos is working very hard to fix everything and Fernando is very able to understand the real need of the users.
Yes you need a training to get the best.
I would recommend 2 renderer.
1.VRAY if you plan to export your model to 3dsmax, Vray would be the safest bet. the support is immense and it is fast and reliable result, also very easy set up. Vray for Rhino is hopeless. if you want to stick to Rhino I would suggest the 2nd one. in Vray you can customize per material base, meaning you have greater flexibility and most of archviz rendering now are done in Vray.
2.MAXWELL if you plan to render in rhino. Maxwell is very famous for its physically correct lighting interaction with material especially metal and dielectric. there is a video on youtube about a guy comparing several renderer, Maxwell is noted to have one of the best metal shaders. the only disadvantage in maxwell is that it takes considerably amount of time to render. but the result is satisfying.
so the choice is up to u 
the best render engine for rhino? hard question to aswer for!
i think the best plugin with a really easy way to add materials and ligths is Brazil(drag and drop and a gui with icons)
but for photorealistic results,i think you must searching for others ones…like Vray(gui not so easy to understand)-Thea render-Keyshot(only in studio)
I think it also depends on the type of object and the scene set up. some rendering are suited for studio set up, some are for still image (no robust motion blur set up), some are good at handling Giga size data, some are perfect for big texture displacement, some supports PTEX, and some are highly customized so that you can write your own shaders. so the choice is also tied to your profession.
in my opinion, if you just started to learn rendering, then pick the one that offers the best support for your job. for example, most archviz choose Vray because arch-related 3D model you can purchase (furniture, street signage, 3D plants, pavement, etc) shipped with Vray Material. while film production tends to pick blockbuster-level renderer like Pixar’sRenderman or Arnold (though Ive seen few production companies uses Vray too). and I ve seen Maxwell used in Commercial clip.
as comparison, 3dsmax and Maya comes FREE with Mental Ray, which is actually a renderer engine that is comparable to Pixar’sRenderman. and I have been waiting for Rhino to have such “bonus” feature
Hi Krsnadas
Just contact me through my email and we can schedule the training.
fernando.rentas@usa.chaosgroup.com