For some reason A Totally Fun Thing Bart Will Never Do It Again appeals to me the most, at least on paper. Though I feel it will be very bad.
The Spy Who Learned Me doesn't sound very special to me, but I get the feeling it will be the best one. The down-to-earth ones are usually the best, except for the format-benders.
I'm not interested on the Gaga one, but playing devil's advocate, I feel like that if they are going to use guest stars they should have big guest stars like this one. It could even work if done right, but it'll probably suck. I defend the Katy Perry episode, though. It was a fun segment and she was funny enough-and hot-in it.
I'm ambivalent about the Nedna thing. I'm not sure if they'll do anything interesting about it.