5 fortune key crate is your credit wallet since you get nothing else but credits. 10 fortune key crate is your starting pack as you get chance of 2 slots for acoins and chance of 2 slots for credits. As for 20 fortune key crate you get chance of credit by one slot and 3 slot chances of acoins. However, the attempts to use 20 option will be slow and double tolling the consumption of fortunate keys so go 5 fortune key crate once you are out of credits, go 10 fortune key crate if you are starting the game and If you are pre-end game then go for 20 fortune key crate.
