Currently, there are 2 types of MCU from Espressif on the market: ESP8266 from 2014, ESP32 from 2016 and ESP32-S2 that debuted in the second half of 2019. Although ESP32-S2 is not yet very popular, it is expected it will replace ESP8266 as a cheaper, more powerful and more secure alternative in the upcoming years.

The table below compares the main features of ESP8266, ESP32 and ESP32-S2

ESP8266 ESP32 ESP32-S2
MCU Xtensa L106 Xtensa LX6 Xtensa LX7
Number of cores 1 2 1
Number of bits 32 32 32
Clock frequency 80MHz 160MHz 240MHz
Coprocessor No Yes Yes (RISC-V)
WiFi 802.11 b/g/n 802.11 b/g/n 802.11 b/g/n
Bluetooth No BT 4.2 BR/EDR & BLE No
RAM 160kB 520kB 320KB
Internal flash No ESP32‑D2WD Only - 2MB No
External SPIFlash Up to 16MB Up to 16MB Up to 1GB
GPIO 17 36 43
SPI 2 4 4
I2C 1 (software) 2 2
I2S 2 2 1
UART 2 3 2
ADC 1 18 20
ADC resolution 10-bit 12-bit 12-bit
DAC No 2 2
DAC resolution - 8-bit 8-bit
Software PWM 8 16 8
SDMMC interface No Yes No
Temperature sensor No Yes Yes
Touch sensors No Yes Yes
CAN No 1 No
Ethernet MAC No 1 No