From what I've read online - Ledger is partially closed-source and a bit difficult to use in terms of usability like upgrading firmware and reinstalling apps, installing/uninstalling apps, low memory etc
That's only really relevant to the Nano S... the Nano X has more storage, so you don't need to worry so much about having to uninstall/install apps
if you use a lot of different coins. If you only use one or two different coins, then even the Nano S is perfectly fine.
Upgrading firmware on both the Nano S and Nano X is relatively painless. There were some issues previously, on the Nano S, that were caused because people had not updated their devices for a while and the latest firmware was not compatible with their old bootloader. As far as I'm aware, there hasn't been any similar issue in over 2 years. These days it's more just "delays" caused by Ledger's "rolling update" policy as the servers take a bit of a pounding when new updates are released due to the number of devices in circulation.
While for Trezor, its open-source. And after that security glitch (wherein seed could be recovered from sram by flashing the device with a malicious firmware) in 2017-18 which they have patched it up via a software (firmware) upgrade - I couldn't find any other major/minor flaws with it.
There is an "unfixable" flaw with the device, that allows anyone with physical access to the device to extract the 24 word seed mnemonic. The
only mitigation to this flaw, is by using the BIP39 passphrase functionality, as that is not stored on the device but used at "runtime" in combination with the 24 word seed mnemonic to derive your actual wallet seed... Trezor recommend users use long and complex passphrases to prevent loss, should your device be stolen etc.
Would like to hear your views on which one is good overall?
I mainly intend to store BTC and Monero. And would be hodling for foreseeable future.
Honestly? Either one will be just fine for your situation... Both Ledger and Trezor support Monero (XMR), as well as BTC obviously. I own both a Nano S and a Trezor ONE. They both have pros/cons. I would like a Nano X/Trezor T, but don't really see the need to upgrade as the extra features offered by the X and T just aren't worth the cost for me personally.
They're both capable devices, compatible with a number of popular wallets (like Mycelium for mobile use and Electrum for desktop use etc) if you don't like Ledger Live or the Trezor web wallet and both support quite a variety of cryptocurrencies.