After a year working with Arnold (Maya) in a vfx studio, I can tell you that it really is a good render, surely one of the best that I've tried. In fact I have tried a lot of renderers, most of them except RenderMan, Maxwell, and some others. Arnold's strongest point, imho, is that it is a very robust renderer that will not fail you at render time. It delivers the render you expect almost every time, no technical issue arise at the last minute like all other that I know. So, pros and cons of Arnold that I can think of:
PROS:
- Targeted at rendering HUGE amounts of data (lights, polys, textures, etc) with minimal RAM usage. Scenes like the spaceship of Elysium were rendered on macs with 16gb of RAM. The more complex your scene gets, the more Arnold arises as the right renderer.
- Very intuitive and simple usage. Artists coming from vray or mental ray get quickly familiar with Arnold, and the Ai Shader is very similar to vray Mtl (or corona's surface shader)
- Fast interactive rendering. In maya, the IPR progressive render is pretty robust, you always have a render of your scene going on while you move, edit and transform your scene.
- It's also easy to integrate in custom scripts and support most of maya's native features.
- Does everything you need for vfx and integration with footage. Intergates so well with MARI!
CONS:
- NOT targeted at Archviz. For a reason that mystifies me, Arnold can get very noisy (like the comparison above) in interior lighting scenarios. Solid Angle has a complete "workarounds" section in its docs for lighting a simple interior... This is the most problematic feature to me of Arnold, that can discourage you to use it as a multi-purpose renderer.
- Can produce fireflies / hotspots. Some rays in Arnold can get very hot - especially with IES - and therefore produce fireflies. Arnold has a clamp in its render settings, but it can become very hard sometimes to track down which light / material produces fireflies and you may need to use non-physical workarounds to overcome this issue.
- No distributed rendering yet, I love when a renderer has this feature!