Ledger supports more coins than Trezor. But ledger, at one time, can support only 4 coins instead with Trezor you can access to all the coins it supports

So if you have coins that Trezor doesn't support,it will be better to buy Ledger

Coins supported by Trezor: https://doc.satoshilabs.com/trezor-faq/overview.html

Coins supported by Ledger Nano S : https://support.ledgerwallet.com/hc/en-us/articles/115005304449-Check-the-list-of-cryptocurrencies-and-tokens-supported-by-Ledger-here