Another write-in for future reference might be Patrick Seitz. I don't know how useful getting him on your show at this point would be, but apparently he's been recording. (apparently, I don't know, it's hard to tell what is fact and what is fiction anymore.)
Of course ANY of the Straw Hats would be awesome. I'm not 100% sure on which ones would have more information (if that's what we're going for here), but I think that Sonny Strait should definitely be up there. He seems like a fun guy.
Another FUNi Rep would be great, but a VIZ one would be as well. Seeing as it is a podcast for both the anime and the manga, a VIZ rep seems fair.
So yeah, what would I vote for? All of them. Geez, I'm no fun. Me and all of my indecisiveness.
Also for the write in: John Swasey(Mr. 0), Caitlin Glass(Vivi), Travis Willingham(Ace) and Laura Bailey(Conis)
Oh and if you can't get Chris for the One Piece Podcast, get him for the Fullmetal Podcast, if that is still alive.
Actually I think that Travis Willingham might be great for the FMA podcast… seeing as he is Roy Mustang. I'd rather have Chris in this podcast and Travis in that one.