As a shop rat in the seventies, standard setup was right rear, left front. It was said the stronger hand needed to pull the rear brake as it's cable always had more resistance, and most people are right handed. It worked for me.
When I outfitted my period fixed gear, I had two brakes but it seemed appropriate to use the right front for my stronger hand and back caliper combined with foot braking on the rear, especially with the period calipers that didn't work nearly as well as what I was used to. After switching calipers on that bike three times now (still not great braking, I am used to more modern brakes) and not seeing much difference in braking between left and right, I now go for the elegance of the curve of the brake housing as it arches so much more gracefully over the stem ... Right lever to front brake for Weinman sidepulls with their lever arm to the left side, and left brake to front with Campagnolo's style of lever arm to the right. Since most of us consider the bicycle as art, the graceful arc of unkinked cable housing in compression at it's perfect minimal length is usually also it's most efficient. Blipping brake levers to check out caliper adjustment is part of checking out the bike at the beginning of every ride and gives you a quick idea of brake setup on an unfamiliar bike.
Happy trails,
Dan Artley in Parkton, Maryland USA