Depending on what sound that you like 

Fiio x7 is cleaner, more airy and brighter, slightly warm.
Cayin i5 wise, more analogue sound, with better ambience, richer, thicker and warmer. more solid and punchy sound

X7 sound stage wider, i5 with better depth.

User interface wise, if you want something like phone, then can consider X7.
i5 user interface is specially designed for i5 to eliminate the interference, and the algorithm of the operating system and music app are optimized for better sound quality. You can still download third part app to use it on i5, connect to WiFi and bluetooth. Just that the interface is a bit different from phone.

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