Zork: Grand Inquisitor

If you're going to play a Zork game on stream, and not one of the text based ones but one of the point and click-y ones, then I think Return to Zork is to be discouraged, as that game has actions you can take on one of the first screens that will turn out much, much later to make the game uncompletable, without any indication. Zork: Grand Inquisitor on the other hand is a higher quality, newer and funnier FMV game that lacks all the irritating unindicated failures. Even the (original CD version, not GOG version) installer is hilarious. Zork Nemesis, the game that takes place in between the two, on the other hand was a for-it's-time really nice Myst-style FMV game, that really didn't have much of Zork to it, and hasn't aged well at all (not getting the Myst multiple remastering treatment might be a reason).

So in other words, among the PnC generation of Zork games, I think ZGI would probably be a better show than either Return to Zork or Zork Nemesis would.