From Trezor Wiki
Main disadvantages of base58 format which has been used in Bitcoin for most of its history are:
- Base58 needs a lot of space in QR codes, as it cannot use the alphanumeric mode.
- The mixed case in base58 makes it inconvenient to reliably write down, type on mobile keyboards, or read out loud.
- The double SHA256 checksum is slow and has no error-detection guarantees.
- Most of the research on error-detecting codes only applies to character-set sizes that are a prime power, which 58 is not.
- Base58 decoding is complicated and relatively slow.
A Bech32 string is at most 90 characters long and consists of:
- The human-readable part.
- "bc" for mainnet
- "tb" for testnet
- The separator, which is always "1".
- The data part, which is at least 6 characters long and only consists of alphanumeric characters excluding "1", "b", "i" and "o".