Involved in the biosynthesis of the osmoprotectant glycine betaine. Catalyzes the oxidation of choline to betaine aldehyde and betaine aldehyde to glycine betaine at the same rate. A + choline = AH2 + betaine aldehyde betaine aldehyde + H2O + NAD(+) = glycine betaine + 2 H(+) + NADH Amine and polyamine biosynthesis; betaine biosynthesis via choline pathway; betaine aldehyde from choline (cytochrome c reductase route): step 1/1. Belongs to the GMC oxidoreductase family.