Square wave / Sine wave is more audible
The square wave will be more audible.  50 Hz is fairly low and most speakers will not reproduce that frequency very well.  Since a sine wave will have only 50 Hz there may not be that much audio reaching the human ear, and even then the human ear will not respond very efficiently to it.  A square wave, on the other hand, will have lots of harmonics that the speaker will reproduce very well and the harmonic frequencies will be spread right through the ideal frequency range for human hearing (300Hz to 3 KHz).