Another left-front lefty here. I generally signal before starting to brake, then put both hands on the bars while decelerating. I use the front brake alone on dry, level pavement and both brakes together on wet, gravelly, or otherwise slippery surfaces. I use the rear brake alone to check my speed on a long descent, to avoid overheating the front rim. If I were strongly right-handed or rode a motorcycle, I probably would go with right-front, which is how my first (1962) Bianchi was configured at the factory.

I think right-rear traces back to Schwinn and the typical American fear of the front brake.