DX50 is $200 from amazon. The x5 is $350.
It's really up to you to decide what you want and how much you want to spend.
To me, I hated the design of the fiio x5 because sometimes it was just a pain to use especially if you have thousands of songs in your playlist. Not fun scrolling through them all to find the one you want. The buttons stick out a little so times they press while in your pocket and the song changes. For whatever reason it also didn't read my cue sheets.
I like the DX90 better because the design is just much more simple and intuitive. But not without problems of course. The USB DAC doesn't always work for some, and no mac support, but hopefully ibasso fixes that soon. And the battery life sucks compared to the fiio x5, but it is user replaceable unlike the x5. No dual micro SD slot.
Honestly, I'd be happy with either because they are both amazing sounding players for the price so my final decision came down to the design. Though I would love a dual micro sd slot, or the much longer battery life, I realized I don't need that much storage and the current battery life on the DX90 is good enough(and replaceable batteries for those who need it.)
Edit: I have the dx90 not the dx50 but everything but the sound quality should be similar. Also it's 4.3 vs 4.1 stars on amazon Edited by bobby12 - 6/30/14 at 9:27pm