While my desire is to make one household system a regular goto system with my family, I truly have the most experience with one of the crunchiest of systems, good old d20!
So based on experience, Pathfinder/d20 is the easiest. Unless a system that is easier than d20 is still easier to run cold than a difficult game to run when experienced, I'd be open to that.
There is a system that just came out that I have hope for, for being easier to run as well as a good candidate for our household family goto system. That is the Pip System from Third Eye Games. We first saw it powering Mermaid Adventures, but that setting didn't do it for me. I wished it was available as a slightly more realized generic system- and lo! Its almost as if Third Eye Games heard me! Here it is! And it's a fine little book that prints on demand quite well.