Hello,
i have Kray and Maxwell, yet i would buy corona.
Corona is very targeted to archviz, as said most engines for Lw are aimed to animation more than architecture.
Octane is good but being GPU is on another league, many want to stay CPU for a lot of reasons. Kray is in a slow development phase and even if it's a good engine, it's a niche tool.
Maxwell is useable in production only if you have big farms (we have 200 ghz farm but it's not enough for our production times), so we nearly dismissed it.
In LW arena we need standards and Corona seems to be able to become a new Vray, given it's absolutely top-notch kernels (better than Vray ones and the state of art in GI solutions).
I know LW arena very in depth, being a long date user and leading a viz firm for 20 years, i know corona would fill a gap here. Finding people with a know-how will be easier, instead of having to teach them LW rendering, and that's a majr point. There's a huge discussion about the need for standards in LW userbase.
Also, as said Lw lacks *the* standard - Vray - which makes Corona so interesting for most, if not all, professional LW users around.
Best,
Paolo