Hi KEITH,

Here's just an advice about some render engines I know.

If you've got the horse power, like a quad-core or better, unbiased render engines like fry or maxwell are interesting.

They are really easy to understand, more over if you know a little bit how photography works. Even the shaders are really simple to get,
probably not so easy to tweak because of the rendertime, but just with basic presets you can archive really incredible rendering.
Of course I'm only talking about stills image, as you need something like 5-20 hours of cooking for a final frame. (a simple image like the little truck
takes only 5-10 min don't worry :)).

Modo has also a really good engine, they are maybe 10 parameters to tweak in fact for the render itself, but the interface take some times to understand.
Same for the shading system which is not very usual (some kind of photoshop layers system).

Actually my favorite render tool when it's about productivity is still this good old fprime for lightwave. They are no surprises and you have a realtime feedback.
Forget hyper realism of course ... and you need to get lightwave workflow a little bit.
It seems that vray is coming with a realtime render too, curious to see it in action !

Of course it's just I personnal taste here =)