I'm a big fan of lightweight, automated tests. Despite that, I still default to manual verification. Usually I do both.

Automated tests omit a certain type of feedback that I think remains important to the development loop. Automation doesn't care about a poor UX; it only verifies what you tell it to.

For instance, I regularly contribute to a CLI that's widely used at $WORK. I can easily write tests to verify the I/O of a command I'm working on that assert correctness. Yet if I actually try to use the command I'm changing, usually as part of verifying my changes, I tend to discover usability issues that make the program more pleasant to use and the tests would happily ignore.

Also, there's certainly cases where automation isn't worth the cost. Maybe because the resulting tests are complex, or brittle. I've often found UI tests to lie in this category (but maybe I'm doing them wrong).

Because of these things I think manual testing is the right default. Automated tests should also exist; but manual tests should _always_ be part of the process.