"{" on a french keyboard is two key presses but at the same time (alt gr and 4), while ^ is two key presses one after the other, which makes it a bit slower. Most editors will also insert the corresponding } when you create a {. That makes in my experience {} faster than ^ and {{}} as fast as ^.

{} is still a common complaint in my circle of programmer friends and everyone has seriously thought even once about switching to an english/american keyboard, but then there's the issue of switching back when writing stuff in french (é by itself almost ruins the idea).