Generally speaking, you can choose backup Mnemonic phrases, Keystore or Private key, but imToken strongly recommends that you backup your wallet using Mnemonic phrases. There are several reasons for this:

1. Although Keystore is an encrypted Private key, it is inconvenient to write the whole code. Generally speaking, it needs to be stored through the network for transmission. Moreover, Keystore often gives users the illusion of security, when in reality it is not the safest method of backing up your assets. There have been many cases of users using online platforms to store their Keystore, which has compromised their assets. 

2. The security level of the Private key is the same as Mnemonic phrases. Both are unencrypted Private keys. However, the Private key is also inconvenient for users to write down, as it is a long string of randomized characters. If you write the Private key wrong, you cannot use it to recover your address. We do not recommend backing up or transmitting by the Private key method.

3. Mnemonic phrases manage multi-chain wallets. Using only one Mnemonic phrase you can manage assets on multiple chains. In the APP imToken 2.0, you can use one Mnemonic phrase to manage BTC, ETH, EOS and COSMOS together.

Whereas Private key and Keystore, on the other hand, store data from different chains separately.  

4. The Mnemonic is convenient for you to write down. We recommend that you use physical media to backup your Mnemonic phrase. This way the backup is completely secluded from the network which effectively prevents hackers from attacking.