My best two for free spins are on Microgaming.
The first one is Ho Ho Ho, and the second one is Twister. They are both for 20 free spins, and can be re-triggered, which is where I always have my luck here.
On these two games I have re-triggered up to 160 spins.
I do the best when it is set on .02 but when that runs dry change it to another demomination. I have won quite a bit of money here...then spent it...hehe