The ones where I know the rules.
Question 22: Which RPGs are the easiest for you to run?
For me it isn't so much the RPG rules that dictate what I play, but the kind of adventures that can be told through the system at the table.
Though if you take this question to mean, rules aside, what is easiest to run? Then it has to be any game where I know enough of the setting to be able to improvise freely. There are a few games I can do that with due to many years of by-in in the past, but I can't see many newer games allowing me to have the time to do this unless they are based in the real world, or near enough!