You know me, I'm an inveterate, unrepentant joiner.
I thought the prison game had a good beginning, though I remember you said you didn't have a lot of ideas for where to go with it.
The PA game sounds fun, and would be an interesting departure from the usual fantasy fare on Enworld.
I admit, I am a little concerned about your workload. In the past you've sort of supernovaed...appeared, exploded in a blinding bunch of games, and then vanished. I realize there are many reasons for this to happen, undoubtedly most/all of them outside your control. This is in no way accusatory. I'm just thinking...maybe take it a little slower this time and see what happens. It may be easier to juggle PBPs with RL events if there aren't so many PBPs to deal with.
That said, only you know your abilities, desires, and situation. If you feel like you can do another, and really want to do another, then I'll support you...by playing.
As for what, again, they all sound good. PA and Prisoners are the most immediately "adventurous" of the proposals, but even Castles seems like it would be an interesting departure from the standard game style, once we're past the opening dungeon crawl.