I've used Lux for only one render so far, to see what I could do with the new Reality plugin for DAZ.  It took 48 hours to sample 3600 pixels and produce a render I thought was good enough to publish.  You can see it here.

I'm hesitant to use it again though.  The biggest problem I've found with Lux is that, while it makes inatimate objects and architectural scenes look absolutely phenomenal, once you stick a Poser figure in there, it looks like a Poser figure.  I haven't even tried Pose2Lux.  I took one look at the UI and my eyes crossed.

I'm sticking with Firefly for now.  I'm familiar with it, I know how to get the kind of results I want, and it only takes a few hours to render a scene on Final settings.