ESP8266-12E is the enhanced version. in comparison with ESP8266-12.
It has the perfect the peripheral circuit. and can enhance the impedance matching.
The output signal is better. both stability and anti-interference ability. has been greatly promoted.
For the user for the choice of ESP-12. it doesn't matter.
The enhanced version ESP8266-12E is fully compatible with the firmware of ESP-12.
It has the additional six pins with IO and SPI ports on the basis of the ESP-12. then develop more convenient. more widely!