Which RPGs are the easiest for you to run?
Low/no prep games such as Fiasco and Powered by the Apocalypse are easiest for me to run because, well, they are low/no prep (the category rather says it all I suppose). There are story games that push the envelope of “what is a roleplaying game?” like Questlandia and the Quiet Year.
Almost any game CAN be low/no prep if you are sufficiently familiar with the rules and have put in some time preparing in the past. I used to run Champions with little preparation because I knew the system so well.