I have no experience GMing, except for solo-play if that counts. But I have been thinking about getting in to it for a while now, so I would be willing to give mutual GMing a shot.
Right now I think I would mostly be interested in some sort of hearth-fantasy fairy tale kind of setting. Less epic quests and grizzled veterans and more of kids getting dragged in to their first adventure. Basically Brothers Grimm rather than Tolkien or Howard.
Probably my favorite game, both as a system and setting(generator), would be Beyond the Wall. I don't think it has a free SRD floating around though.
I have also had
Shadow and Fae 2e sitting on my hard drive for a while and would love to try it out. It is PWYW, but does not provide setting information other than what is implied by the Tales(classes) and the artwork, not even a default list of monsters.
SWADE is somewhere on my bookshelf, but I am not super fond of it. Played a lot of it solo though, so I know it fairly well.
FATE always kind of interested me, but I am even less confident in GMing that as I have never played it or anything like it.
Finally I am always open to experimenting with some minimalist/FKR kind of approach.