To me the perfect combination would be to have a large number of Earth habitats combined with a large number of Rainbows. Kind of a turbo-tortoise and hare approach. I was fortunate to already have a lot of Rainbows and a lot of habitats because I was at level 30. So I decided to invest a few bucks and set up the CGCF. I spent about $125 over a few days and had things where I thought they were just about right. However, a complication arose - I wanted to resurrect my favorite island, the Nursery Island, which meant I had to greatly reduce the number of habitats being used by the CGCF. Fortunately by then the Hibernation Cave had been introduced and, since I'm in a situation where I can pick up coins frequently, I opted to put most of the Rainbows away and concentrate on the high level producing Panlongs. So I presently have 8 Earth habitats with 24 Panlongs on the Asian themed island (thus the name) that produce coins at a prodigious rate.
I then discovered the one or two hour cycle breeding of Air and/or Sandstorm dragons produced at an even higher rate for a very modest cost in gems. So I combined that with the Panlongs to form the final CGCF as you see it now. As a result I should be able to achieve gold shrines in a reasonable period of time at a reasonable cost, something that seemed impossible when I first did the calculations.
Forgive the opus - I just woke up from a nap and wrote this while my head was clearing.