From developing in them, each has it uses.
The calendar is more suitable when dealing with a single resouce as it can show more detail and isn't just a thin single line across the page.
The scheduler is for when you are dealing with multiple resources and allows the easily see the timeline across the page and separate each resource line down the page.
So depending what you are dealing with, depends on which one is best. Also, have a look at the demos for each of the control on the site. It gives you a good idea of what each looks like.