--> For_Due The Arduino Due has three additional 3.3V TTL serial ports: Serial1 on pins 19 (RX) and 18 (TX); Serial2 on pins 17 (RX) and 16 (TX), Serial3 on pins 15 (RX) and 14 (TX). Pins 0 and 1 are also connected to the corresponding pins of the ATmega16U2 USB-to-TTL Serial chip, which is connected to the USB debug port. Additionally, there is a native USB-serial port on the SAM3X chip, SerialUSB'.
--> For_ESP32 There are three serial ports on the ESP32 known as U0UXD, U1UXD and U2UXD all work at 3.3V TTL Level. There are three hardware supported serial interfaces on the ESP32 known as UART0, UART1 and UART2. Like all peripherals, the pins for the UARTs can be logically mapped to any of the available pins on the ESP32. However, the UARTs can also have direct access which marginally improves performance. The pin mapping table for this hardware assistance is as follows.
UART RXIO TXIO CTS RTS UART0 GPIO3 GPIO1 N/A N/A UART1 GPIO9 GPIO10 GPIO6 GPIO11 UART2 GPIO16 GPIO17 GPIO8 GPIO7
Having said that, the UART drivers that I recommend to use don’t have this level of optimization built into them and as a result, you are pretty much free to use any pins you choose.