Arnold is "out of the question" if you want the best tool for the job, that's all. It doesn't have any kind of Interpolated GI or solution baking, so it's really slow for archviz where you frequently render the same camera angles with nothing moving, for days. Arnold has to sit there and cook the GI over and over again for every single render - and that's absolutely horrible for flythrough animations, b/c archviz studios do not have, or want, big render farms.
I'm personally in VFX - and I'd put Arnold in 3rd place at best. Yea it has all the nerdy stuff that programmers like to play with, but that's putting the cart before the horse - if it takes 4 times longer to render, yet it can't render any things that the others can't, then you're either going to blow more money unnecessarily, or you're going to cut quality... unnecessarily, and/or push all your deadlines. Most shows that I've used Arnold on have cut out raytrace reflections and some GI for the sake of speed. DD and Method both use Vray, incl. for Marvel movies, with all the raytracing, so it's obviously a good choice for VFX. I would not be surprised if Renderman was better, but I haven't used it since they switched to raytracing, so I can't comment on it - but I can't imagine that Arnold is better.
