What memory location should I use?

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)

• /tmp
• /var

Non-volatile memory (persistent through reboot/power loss)

• /etc/luvitred/store
• /mnt/data/luvitred - note: only on CloudGate LTE

External memory

• /mnt/sd* - USB
• /mnt/mmcblk* - uSD card

(*) different letters for each mounted drive