I believe, by Most of the people, Bach is considered better. Vivaldi has good pieces but I believe Bach has more good pieces. For that reason, I see Bach better. This is my opinion.
Most Helpful Girl
I like Bach more but its hard to choose who was more intelligent0
Most Helpful Guy
The mathematics contained in the fuges alone justify my voting for Bach. Same goes for his works for pipe organ. The pipe organ was THE musical invention of the time (think synthesizer, lead guitar, bass & drums all showing up at once and played by ONE guy!)
Vivaldi is cool but Bach is my main classical man.
For an interesting treatment of the mathematics I mentioned, this is an excellent book: