Bach's music seems at times almost mathematical. Consider the fugue which was an almost formulaic.. or his magnificat which contains the mathematical aspect and incorporates the voice.
Bach was able to write music in a similar style given any melody. He could even write a fugue on the spot.. given a note sequence.
When it comes to variations on a theme or consistency of style. Bach was better.
Mozart's music is considered to be more emotional than formulaic. His music such as Lacrymosa(requium) and Achs Ich fuhl's are 2 examples of minor pieces that Mozart demonstrates his passion in.
Mozart also has a less serious side.. which is evident because he wrote a lot of music as a young man. He wrote songs like the Papageno/Papagena duet in the magic flute.
Typically Mozart wrote based on the emotion he felt... or the emotion which told more a picture.
Both Bach and Mozart had a different style of composition.. so it is difficult to select a better person.
Myself, I prefer to listen to Bach.. as i enjoy the intricate harmonies woven into his fugues and fantasias.