If you plan on using it as an alternative engine for Daz and with the focus on human characters then, in my opinion the best option is Octane.

I use Thea, wich is a great render suite and i've tryied Luxrender, Cycles and Arion (ex Fryrender) but once you have a good material for skin, wich there are quite a few examples around, Octane is the most consistent in getting good result under different light conditions, and by far. 

I can't tell for Arnold, but i remember seeing around a pic comparison between it and Octane and there wasn't much difference.