What is the best Reel To Reel machine ever built?

Everyone who has listened to master tapes or dubs knows about the well balanced sound they provide. But it is also important to have a fine tape recorder or playing machine to enjoy the tapes' qualities in a good system.
Maybe my question was raised once before but the relevance of the topic is now greater as the tapes are back to more and more audiophile friends, especially those who are owning excellent phono chains.

I have seen many big & professional machines being recently offered and sold on e-bay, Audiogon and other platforms and I am discussing within a small group which machine is really the "holy grail" among the R2Rs. So why not here. I am interested in findings.