Reasons I use Corona:
1 - Lightmix, LUT slider, and all those other features VRay hasn't quite rolled in yet.
2 - User experience in Corona. One thing that struck me from Ondra's talk is that he thinks about the user experience from the inception of a feature. Vlado's approach is kind of 'How fast can we roll this in because we have power users\studios who need it ASAP' which is totally legitimate, of course! Ondra seems to think 'How do I make this tool foolproof and really solid before releasing it.' I think that's one of the biggest reasons Corona is so successful and why I choose to use it most of the time (I own both.) Just look at Bloom and Glare in VRay vs Corona. VRay's B&G might have more features, but (for me anyway) it's hard as heck to use. If I remember right in VRay the glare especially is affected by render resolution, which made it a moving target. Same thing with VRayEnvironmentFog vs CoronaVolumeMtl, Corona gives me the results I want every time.
3 - Realism. This is more my personal conspiracy theory than anything else, but I find that Corona gives me slightly more realistic results, even in the earliest stages of a scene. I know people post these 'apples to apples' comparisons where you can't tell the difference, but still I see it in my work. Might just be me, personal bias, etc. but I find VRay gives me a subtle CG look...even when using the 'PBR workflow.'
4 - Community. The Corona forum is way more active these days, you can't discount the importance of community.
5 - Glitches. More often than not I get frustrated with VRay's IR because it doesn't update. It's a ton better than it used to be when it first came out, but I'm always surprised by little glitches. Corona seems to always update with scene changes and be more stable. Or something is supported in VRay production but not VRay IR...yada yada.
Anywhooo...just my two cents. I still love them both.
