Are any parts of Excelsior in San Francisco more safe than others?

I should add a second thought: I think of Excelsior in general as reasonably safe. More depends on you and how you're acting. If you're out at night with an expensive cell phone in your hand, and oblivious to your surroundings, you could get in trouble anywhere.

I'd spend a bit more time looking over my shoulder in the small chunk of the Excelsior that includes Sunnydale Avenue. This leads to the Sunnydale district -- which isn't part of the Excelsior, and is one of the more problematic neighborhoods in San Francisco.

Otherwise, the streets farther from Mission and closer to the west end of the park might be just a tad better.