What memory location you should use depends on your application and a couple factors.
Do you need the data to be reboot persistent (non volatile)? Or do you want to start from a clean slate after a reboot (volatile)?
Volatile memory (temporary)
Non-volatile memory (persistent through reboot/power loss)
- /mnt/data/luvitred - note: only on CloudGate LTE
- /mnt/sd* - USB
- /mnt/mmcblk* - uSD card
(*) different letters for each mounted drive