The ESP32s are nice chips, but the STM32s are also really nice to work with and will work fine for this task. Changing to an ESP32 wouldn't make any real difference to the user so the choice is moot really.
I've designed products around both CPUs and they're both pretty nice. The STM32 has somewhat better documentation, has cleaner low power modes and is a bit simpler when delving into the nitty gritty details. The ESP is more powerful and has some nice if complex features but I don't like its low power handling as much.
Overall I think I'd choose the STM32 for this task since it's a little easier to make small, battery powered devices with it.