Here's my 2 cents worth about older Japanese motorcycles.
The big difference between Honda and the other three Japanese companies was that, until recently, Honda supported their old models with parts. Because of this, parts availability was and is pretty good, even for some obscure models. Unfortunately, they decided a few years ago to not to support models older than 1971, so now supplies of new parts are drying up for the old stuff. I believe Honda had the resources to be a little better about having the bugs out of their products before they were released. There were exceptions, of course.
Yamaha is the worst for parts availability, in my experience. I had a '93 600 Seca that I got for my wife that I had trouble getting parts for in 1996. I sold it soon after. If Yamaha doesn't care about their bikes, why should I?
It looks to me like Honda's fit and finish on older bikes was a couple cuts above their competition. I've seen a lot of KZ and GPZ Kawasakis with some hideous welds, lots of spatter and undercutting. More care is taken with welds on a typical tractor.
Suzuki had their problems, but has always come up with some great bikes even though they didn't have the resources (money) that the other three did. They weren't afraid to try something different. They have always had some interesting engineering.