Are you experiencing this during the update period?

Some of my websites have dropped in rankings during this Google update, but some have gone up. I know this is meaningless during the update.

Currently, the search results are different when I'm logged in to my Google account and when I'm logged out. The same thing happens when I log in with multiple Google accounts of others.

Which one should I assume is correct?

Google results can vary based on the location, search history, google account, etc...
Nothing new here, it has been the way for a good while,

You can use an incognito tab with VPN/Proxy to get the most accurate results,
Or simply use some SERP tracker to do the work