Hello,
since you will spend most of your time in France, you should apply at the French embassy; however, considering that you really just travel quickly through, it does not really matter, I would pick the embassy that is closest to you and with shortest lines.
One thing to remind about, you will spend a lot of time on the road. Brussels to Paris = 350 km. Brussels to Munchen = 750 km. Munchen to Vienna = 500 km. Vienna to Geneve = 1200 km. How do you manage to travel such distances and at the same time to enjoy the country in just one day per country? I doubt one day per country is enough.
Belgium, Germany, Austria, Italy, Switzerland, and France are part of the Schengen zone, see here
Schengen zone.
Dani