Best is not defined.
But if id really would need rank renderers then the easy 2 best ones are
Pixar renderman (and yes allways get the pro studio for maya)
Mental Ray
Not just for animation but overall, prman is VERY hard to beat*. In that order, after theese come a number of other specialized renderers id say the next best one is
Gelato, but its discontinued
And then comes vray and brazil, mantra and the renderer lightwave uses come next in line. Allmost impossible toe distinguish from each other.
I would disagree
There's nothing really special about vray, its no more realsitic than mentalray, or prman. Its just prepackaged with easy to use interfaces that are good for certain things. If you find it impossible to match vrays quality with other renderers than that's just because you dont know how to use renderers in first place. Vray is OK.
This bring us to the point number 2, no amount of money will make your renderings good fast, goodloking, realistic and so on. Only skill and knowledge will bring you to answer why its better. That is to say by bring into a software you should ask yourself do you buy a good product for you to evolve on or do you buy a good product to. So either you buy and are ready to pay for all the included ability or not.
*sure its PAINFULL to set up for global illumination. But on the other hand it can pump so much geometry on the screen that its scary. Just the seer volume of all it does is daunting. It can do it ALL, and i do mean ALL. but its not for the person who seeks a one push button solution, its for the one that has a tech department thats willing to your OWN push button solution. I especially like its caching architecture wich can cut down 1/10 of the rendering speed. And offcourse its motion blur ability. Its MAJOR downside is that you basically have to reateach every user in the shop once you switch, form lowly modeler appentrice to the animation god.