User blog comment:Malcolmxofart/Frontier Hunter event?/@comment-24796771-20140409223920/@comment-24699201-20140410013632

I typically get four units per run in Paradise. Usually three random idols, plus one random unit. The lowest I've ever gotten was two units (one idol and one random), but four units is my average.

I do agree though, Paradise is not very economical. I was lucky in that I managed to completely stockpile almost everything I'll need for (hopefully) a few months in a few days since Paradise event is open, aside from water units (which is ironically why I went in there in the first place -_-). I literally spent about 12 gems, just doing Paradise runs (Sprites and Idols), trying to get 2 Idols and a Sprite. Got everything I could possibly ever need...except the water ones. Finally stopped after I got the second water Idol. But, I wont be needing to worry about the other elements for a very, very long time.. lol

However, I do understand that not many people have the...freedom to spend gems that liberally, so, yeah, from an Economical standpoint, using St. Lamia is your best bet for farming Idols. The fourth area (as in, second from the top) is usually the most economical energy vs. experience wise (i.e.  The Banished Fire Dragon,  Ruler of the Water,  Maiden of the Trees, ect.).

Unless your really unlucky, you'll typically net an Idol every either 18 or 27 energy (for me, its usually 27 energy).