I have a Trezor 1 and a Ledger Nano S.
The Ledger has been abandoned. There's something about the way they operate I dislike. In this game you should be humble and open and they certainly are not. Trezor's attitude is better and more communicative so they're the ones I stick with.
I am starting to wonder about the future of hardware wallets, more holes are found every day, but since all current ones need physical access to exploit I'm not going to sweat it until that changes.
Ledger is a much bigger company which I think influences how it's ran compared to Satoshilabs.
If someone owns a lot of different altcoins Ledger supports more than Trezor.
Trezor T supports 1392 different coins and tokens:
https://trezor.io/coins/Couldn't find any up-to-date information regarding the number of supported assets by Ledger.
One of the negative points for Ledger is the Secure Element chip not open source
For now, Ledger is definitely at an advantage because there is no such vulnerability - if there was one, Trezor would surely make it public. But what some people don't like about Ledger is the fact that it's not open source, for which Ledger again gives somewhat logical reasons.
https://blog.trezor.io/introducing-tropic-square-why-transparency-matters-a895dab12dd3