There is not the best single box CD player, as a component of a systems it depends of the rest of the chain.Said this, I think that EMM LABS CDSA, Reymio, Puccini, Naim 555 , Memory player are among the best, I have not heard PD MPS5.
But perhaps the question is: I need to pay 2 or 3 times more for to get a little better sound? When we make this question, we are talking about relation price/quality, that is a very different thing that maximum quality at any cost, and logically the answers will be differents.
Jean Hiraga, the french engineer who was the first to talk about sound in relation components, and designed great tubes amps that were on Stereophile class A, one time said: if you have a great system, that give you the 95% of the posible quality achievable, to upgrade it to achieve the 96%, you surely need to expend twice the price, but if you have a system with quality 60%, then to achieve 65% you only need to expend a little more, the conclusion is: when we are talking about great systems or components any small increase in quality must be paid with a lot of money.
I have heard dCS Scarlatti system, I don´t want to say that is the best, but surely, because I heard it , take a seat, with one integrated amplifier, I don´t remember the brand but perhaps Arcam? and speakers that I don´t remember,and the sound were incredible, and after also with systems with BAT, Spectral, Soulution, FM acoustics, said this I want to say that it surely sounds better than the EMM labs combo, but I don´t want to expend the money to achieve this small amount of better quality, but if money wasn´t the question, I will buy it to achieve what I think it´s the best, and for one single box, surely I will buy Memory player, it has the futur inside.