Can I set a default Login for a website?

If you save multiple Logins for the same site, there is currently no way to set one as the default to use every time you Login or for when you use the Fill Login shortcut (it's Command-\, and you can change it under Preferences > Extensions in the main 1Password app).

There is, however, a workaround you could try that involves hiding all the other Logins you don't want to use regularly in your browser. You can still open these Logins and automatically sign into those sites from the main 1Password app, but for your general day-to-day use, this will allow you to use your default Login quickly from the 1Password extension or the Command-\ shortcut. Here is how to properly setup your Logins for this:

1. Open the main 1Password app and select one of the Logins for a site that you don't want to set as the default
2. Click 'Edit' at the bottom of the window and click the 'Display' menu that appears
3. Choose "Never Display in Browser", then click Save at the bottom of the window
4. Repeat these steps for each of the Logins you don't want to set as the default

From now on, when you click the 1Password browser extension or use Command-\ to quickly log into a site, 1Password will default to the one Login you left alone and instantly log you in, just as if you only had one Login for that site.

If you want to sign in with one of the other Logins for a site that you have hidden from the browser extension, you can open the main 1Password app, find the Login in question, and click its URL at the top to open the site in your default browser and automatically log into it.