I feel that the 400 series on a work day are very safe. The 400 series on a weekend where its the people who don't commute come out and all have the same scared mentality. The 400 series have their own etiquette. If you don't know it, then yes its scary. Onramp/off ramp queueing, lane merging/leaving space, mixed signals, truck drivers. Anyone who has commuted via major highway in a 9-5 job for a couple months will know what I'm talking about.
Intersections, especially high density areas, are a nightmare. A whole lot of people who don't know/don't care about the rules of the road. Drivers, pedestrians, cyclists, taxis.
Suburbs are typically also photo radar community safety zone boring straight lines so lets skip that as motorcyclists.
Back roads you gotta worry about the roads (gravel, mud, unmaintained) and the farm equipment. Still the most fun option which leads to a different set of 'dangerous' criteria.