Raspberry Pi Pico

Great price and small form factor. Easy to program in MicroPython or CircuitPython.

I decided to learn MicroPython and this is what I picked. You might have a challenge finding drivers/libraries for certain peripherals. If you find a MicroPython library, it might not support the PICO. If your projects a mostly sensor module based, check if CIrcuitPython or MicroPython will be a better choice I've been finding that because it's still new, much of the information available is of a good quality though there are some "mostly complete" tutorials out there where the "download the official driver" link goes 404. If this will cover your needs, compare the price to the datasheet - it's very impressive.