I like that there are a huge variety of them and they can be directly soldered to a PCB assembly with their castellated pads. I have many of the variants. I have a few of the newer ones that I haven't had a chance to try yet - ESP32C5, RA4M1 and nRFL15 Sense. I like that most of the newer boards have battery support. It is also nice that they are compatible with Adafruit QT-PYs. Adafruit has some nice add-on boards and a couple of RISC variants.
Can't beat a good rummage around in a shoe box 
"...I know you are in there somewhere..."
unlabeled in a shoe box:
Took me about half an hour to find out which shoe box.
