Vray vs Mental ray GI

If it was an interior scene I would suggest VRay, even though I am generally 
biased to MR. And this is, only if that interior was an animation. Since 
its outdoors, I'd say MR all the way. It blows VRay in speed/result, imho.

Than again, MR can’t do every specific frame recalculation, so while MR is 
faster on a single image, I don’t think its faster 10x to justify using it as 
opposed to every 10th frame as Joseph suggested in VRay.

The result you get with MR will be far superior even in 1per1 not to mention 
in 1per1/10, but that might not be too big an issue for you.

It boils down to what you want/ expect/ are used to in your workflow.
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EoDEo

Ideas drift like petals on the wind. You have only to lift your face to the 
breeze.