I'm not sure what this "theory of always unclipping the same foot" is, but I don't recommend it.

You should be able to unclip both feet. There are many situations, in real-life traffic, where you may need to unclip your "not-so-sweet" leg.

Practice both...

Good luck with the pedals. I've found that mountain SPDs (recessed cleats) are the easiest to unclilp of, when at their light-tension setting.