which should I choose? JXD S7800B or S5800

[Made in China]

Happy Chick is a frontend for some of the more popular illegal ROMs and outdated emulator versions. You have absolutely nothing to check there - if you really wanted, you can get both of those things with ease on your own.

The problems in question is the battery drain when in idle, plus the imprecise battery indicator, the fact that the SoC takes ~10 minutes to understand it needs to ramp up the clock speed to keep up with applications, problematic Wi-Fi, limited support for BT dongles and any other feature introduced after Android 4.2 and iffy sound. Those are just the things off the top of my head.

Do not bother with the S7800B. Also do not bother with the S5800, as it is terrible for a phone, and both are pricey more than the newer competition. This is coming from an S7800B owner.