I am currently using the following scheme for single-sig + passphrase:

location #1: Seed backup location #2: Seed backup location #3: Passphrase backup memorised: Passphrase

In this scheme one back-up can be lost and funds still retrievable, so it's like a quasi 3-of-4.

I am considering an upgrade to a 2-of-3 multisig:

location #1: Seed #1 + xPub quorum location #2: Seed #2 + xPub quorum location #3: Seed #3 + xPub quorum digital: Various xPub backups

The main advantages of 2-of-3 in my case would be that it's more resilaint against evil maid attacks (as multiple devices need to be compromised), and I'd be unable to forfeit the keys while under duress (as nothing is memorised).

The main disadvantages of 2-of-3 in my case are complexity and potentially privacy (as the xPub quorum reveals one's balance).

I go back and forth on the decision to upgrade. I think SS+P is fine for now, but at some point we may be living in a more adverserial environment where KYC data is leaked and BTC is worth x10 today's price. I would certainly appreciate the extra security in such a scenario.