The musicals I have watched the most are; Singin' in the Rain, Hello Dolly, Guys and Dolls, All that Jazz, Little Shop of Horrors and Cover Girl. But, like everyone I here I have many favorites. Besides the wonderful songs, the plots of these musicals also play a major roll in repetitive viewing, costumes, and the dancing and the people doing the dancing.
I also shamefully love The Worst Witch, not a true musical, but they sing a fair amount.