For me, there's only one clear answer to this question; it has to be, most definitely, without any trace of doubt ... the room in which "soda that never goes flat" is invented. No, not because I want a fizzy beverage, but because you begin to levitate upon drinking it. Performing flips in the sky is so much more rewarding than a few sickly treats! Oh, and the whole spinning-blade thing that would horrendously blend you into a rather unsatisfying Wonka Smoothie can easily be avoided by burping - no danger whatsoever! I hope...
The never melting ice cream room, fantastic. Just carry them around anywhere and you'd always be ready.