I bought my Pioneer XDP-300R this past month and it was a decision between Onkyo DP-X1 and the 300R.
I chose 300R in the end because of the loose headphone jack issue from Onkyo and 300R was just accessible at the time.
This is my first Hi-Res player so I can't really provide much comparison but I am going to highlight a few observations I have made so far.
1) Solid build, easy and user friendly android interface
2) Power Output: I use this to drive my Campfire Audio Jupiter. And it seems to be doing the job and I am usually fine with volume around 70~80 sometimes higher or lower depending on the audio source.
However several people have pointed out that this may not have enough power to drive headphones by itself and I think it is true. (just pair with an amp and you are good to go.)
3) Sound Quality: It's spectacular. Again using my Jupiter as a baseline there is just nothing to complain about
4) Battery Life: Because of the android system it tends to drain fairly quickly even when it's left idle. That's also because I don't turn off all the background apps. Battery life would probably be more sustainable if you turn off everything else.
Overall, the player has been great. I just have one really frustrating issue regarding the official Pioneer case for the 300R.
THIS THING WON'T BUDGE AT ALL WHEN I TRY TO REMOVE IT.
When people say it fits like a glove, it totally does. And if you already have your memory cards inserted and do not have the intention to ever remove the case again, then you are good to go.
But I made the mistake of putting on the case without all my memory cards in and I am now stuck with a case that would most likely need to be cut (Which I think someone has done it before already) if I want it to be removed again.
You have been warned.
(I am going to try to add more comments on the player as I spend more time with it)