Speaking from experience, Hondas and Kawasakis service manuals are both very straightforward but Honda has an edge in detail and completeness. Harley manuals are solid as well, but working on a Harley requires learning some new concepts as a result of their ‘unique’ engine/transmission arrangement.
Overall, the biggest problem you’ll face with Harley maintenance will be vibration-induced unplanned automatic parts disassembly. But with copious amounts of blue Locktite™ and the advent of filament-less LED light bulbs, that problem is completely manageable