I first got into Raspberry Pi Picos, but I've also been experimenting with Esp32's and some of the nRF chips. I mostly do CircuitPython on them but Arduino is a supported platform on those I believe.

I got a couple of RP2040 boards recently and I'm amazed at how easy it is to just get stuff done. Between the native usb support and the circuit python support it's been a breeze. I just got a couple of boards up and running uart in a daisy chain. It was intimidating, but the circuitpython docs made it relatively simple.