The Diatonic harmonica standard 10-hole is the best for nailing that wailing Blues sound, and it's the most common harmonica heard in American popular music. It's also the easiest harmonica on which beginner's can learn to play and start sounding great right away.

With regular deliberate practice, you can expect to be playing simple pop tunes within around 3 months. Within 6 to 12 months, your technique will improve and you will probably be able to work on bending notes (a very important skill for getting the best out of a harmonica).

There is no difference. A harmonica is a mouth organ. There is another instrument called a glass harmonica that is not a mouth organ, but a musical instrument consisting of a series of rotating glass bowls of differing sizes played by touching the dampened edges with a finger.