Is there a motorcycle touring boot that rises above all others, in terms of being the BEST boot for touring?
Maybe, but then, again, maybe not.
You need a waterproof, lightweight, comfortable boot for long distance biking. Ideally, the boots should be so comfortable that you will not want to switch to another pair of shoes for walking around during sightseeing stops.
And so while there are a number of good choices, the very best pair for you will depend on fit. You want to find a fit without any areas of pressure or rub. Unless you are a dedicated cruiser rider and have foot boards, you need some extra protection on the top of your left boot - where the shifter peg hits. I like the Icon Women's Standard Boots because they are modeled after typical hiking boots, but have added features that render them perfect for biking.
I like lighter-weight boots because my knees get tired at the end of a long day, and I don't want to pick up feet that feel like lead. Climbing a set of stairs to your hotel room with a feeling of having concrete boxes at the end of your legs isn't fun. For lightweight leather boots, I really like the River Road Women's Low Cut Ranger Harness Boots.
Fashion is definitely not a priority. You want fit, function and flexibility.