Compared to most other American cities. One thing to note is that SF != SF Bay Area. As a one-time resident of many US cities and suburbs, SF and seattle are among the best, but the old north-east are better. The general trend is that if the city matured before cars, its walkable (eg NYC). I've lived or spent considerable time in Boston, SF, Seattle, Cleveland, San Jose, NYC, DC, and others. I don't have much experience visiting non-us non-canadian cities though, so I can't compare.

SF is basically 7mi x 7mi - you can literally walk across the whole thing if you had to, so all neighborhoods are close by definition. But most of the city is also a grid which makes for easy navigating (with the exception of some of the hilltops where the road follows the terrain). There is great public transit, but its centered around the "valleys", so you still have to walk up which kinda sucks. Beyond the geography, SF has one of the better public transit in the US (maybe top 5, after NYC, Chicago, DC, maybe tied with Boston). The city is not made for cars - most places don't have parking, most commercial establishments go up against the sidewalk instead of putting a parking lot along the road. Its highly varied street-frontage that makes it appealing to look at (as opposed to long stretches of featureless walls). Regular crosswalks, narrow roads (so its easy to cross and cars go slow). All the street-level stuff you'd want but wouldn't find in a post-war American city.

Seattle is similar to SF but "less" - crucially though, seattle culturally accepts a post-car life. The city feels like a post-war city that knew what it was doing. The city is really green-lighting lots of development downtown to make a very walkable urban core (as opposed to sprawl). It has a much more nascent and mediocre public transit system, but its there and its growing. Seattle has narrow (but not as narrow as SF) roads, and dedicated sidewalks and bike lanes and all the other "not-car first" features built out in the densest areas and being added slowly in the periphery. The urban planning is clearly not focusing on the car throughput but instead the livability of the neighborhood for residents when changes get made.

NYC is probably the best American city to live without a car, due to the extensive subway system, but also it's regular grid makes it easy to navigate (in Manhattan at least). You'll have everything you need close to you (eg groceries), and extensive transit to get somewhere far. Every road has crosswalks and lights to keep cars under control and minimally in the way. Its so dense that the street fronts aren't used for parking and instead feature the building right against the sidewalk, often with commercial activity (restaurants, cafe, shops, etc).

I think Boston and other north east neighbors are pretty similar to NYC, just smaller cities so less "stuff" integrated into the grid/transit coverage - which increases the odds that the thing you need exists in a car-only area. I don't drive and I couldn't function in Cleveland, but Boston/NYC/SF/Seattle are fine. Providence RI (small city south of Boston) is too small to have a built-out public transit system, but once arriving in the city you can do most day to day things on foot, but you'll need a car to travel across the city or long distances conveniently - but its no where in population compared to NYC/Mexico City or even SF.

I think the deciding factor for walkability is how built-out the city was in the pre-car era (which may vary nation to nation and city to city), and how accessible cars became to the population. Eg. NYC, Paris, Mexico City predates cars by many years, so of course they'd develop alternatives. Meanwhile, LA grew proudly through the automobile, so people don't want to change the city to make it walkable.