opinions differ. i'd never claim to have been to *every* "walkable" city in the world, but i've been to more than a few that are commonly considered standouts in that respect and i'd hold boston's street-level exeprience up to (or beyond) those of barcelona, paris, san fran, london, shanghai, rome, etc. the weather presents challenges in the winter, of course, and like most u.s. cities (until recently) open-container consumption isn't allowed, but i'd say walking around boston in the spring/summer/fall pretty much can't be beat.With all due respect, although Boston certainly has better "walkable, street-level engagement" than most cities in the US, placing us above "pretty much any other [city] in the world" is a stretch for me, imo. You can get the experience Boston offers and better in *most* Western European cities, to say nothing of cities in Japan, Korea, Taiwan, etc.
Heck, you don't even have to travel that far. Canada and Mexico both have several phenomenal cities for walking and streetlife.
To build off that (because this is a discussion I can actually contribute to), the reason fall is better is because the tree is entering dormancy, and less stressful than a spring planting where the tree is putting most of its energy into new top growth. In the fall, soil temperatures are still warm enough to promote root growth, and there is more precipitation and less evapotranspiration. The root development is really key for preparing it for the coming growing season, where there will be less precip and more evapotranspiration. I would imagine it to be even more important in an urban environment.Deciduous plants and trees are best planted in the fall. (Evergreens in the spring).