Fastest Communication from NodeMCU to Arduino Nano
If it comes to speed and reliability you have to choose an interface that is handled in hardware on both sides. For the arduino nano you have the following options (nodeMCU supports all of them):

UART:

not very fast (order of 10kbit/s), but it's full-duplex (asynchronous communication in both directions)
implementation is trivial due to Serial.h
long distance (order of meters)


I2C:

not very fast either (order of 100kbit/s), but not full-duplex
implementation is straight forward because both slave and master are implemented in arduino library
only over short distance (order of cm)


SPI:

quite fast (&gt;1Mbit/s), full-duplex
implementation might require some experience (as far as I know, slave mode is not supported by SPI.h)
long distance (order of meters)



Which of those is the best option still depends on your specific requirements, but personally I like SPI very much because it is very fast and stable.