What is the difference between ESP32 and STM32?
As others have mentioned, ESP32 can be utilized if you’re only interested in connectivity (BLE and WiFi), whereas STM32 has a wider range of applications. STM32 + Other chip-sets are frequently used in products to accomplish communication and sensing applications.
What is the difference between ESP32 and Raspberry Pi?
The ESP32 runs on the RTOS operating system, while the Raspberry Pi runs on Linux. So, depending on your expertise and learning styles, you should pick one or the other. Although the ESP32 appears to be a simpler device, in theory, there is a lot more information on the Raspberry Pi on the Internet.