Which one is right for you?
Aside from construction techniques and steel types, the main difference between the A-type, B-type and SR-1 is 'the feel’ in your hand. The Tobisho A-type feel a tad bigger in the hand and the deep curve on the handle snugs them tight into the palm of your hand. My brother, also a gardener, and a fellow with medium-to-large sized hands, recently tried out the A-types for the first time and he preferred them to the SR-1s. I personally prefer the SR-1s or the Niwaki GR-Pro B-type as I find they fit my slightly smaller, not-as-strong hand better.
Ultimately I think the best way to choose your secateurs is to try them in person to test the fit, length, weight and spread. You want a tool that sits comfortably in your hand, isn't too long or too short, or too heavy or too light. And think about how you use your secateurs - are you rough or careful with your tools, need an all-rounder or want a more refined tool?