I was debating the same thing a few months ago but cannot afford Octane right now and the render times I see people posting for Lux are also prohibitive to me so I prefer Firefly especially with Bagginsbill's environment sphere which is free:  https://sites.google.com/site/bagginsbill/free-stuff/environment-sphere  If you don't know about it make sure you check all the links he gives.

Some other lights I've found very useful:  http://www.renderosity.com/mod/bcs/index.php?ViewProduct=89899

http://www.runtimedna.com/SunLIGHT.html

I'd say play with these to see if you can get the results you'd like.   Lux and Octane will still be available :)