Corn is okay to learn in, but it doesn't represent the best. Crud is hard on the knees and body in general. This is not an optimal snow condition for beginners. When you walk across crust, your boots will often break through and sink to the bottom. Crust can get broken up and become crud.
Avalanches occur when the soft snow under crust collapses.
This is by far the best surface to learn on. Most green runs and many blue runs are groomed regularly at most resorts. This is a very common condition during cold winter months. Hard pack is great to learn on, although it is a little more difficult to learn to execute clean turns in. You often hear ice scrape beneath skis and snowboards, so you know it's there even if you cannot see it.