WHAT HARMONICA TO BUY?
If you don't already have a harmonica, a good place to start is to get a *key of C 10 hole diatonic harmonica* - this is a Hohner Special 20
But there actually are other shapes that the 10 hole harmonicas come in, such as the Hohner Golden Melody:
As you can see, the Golden Melody has rounded edges and the actual mouthpiece area is a little wider.
Because of health laws, you aren't able to try out harmonicas beforehand, and the reason this is a point to be considered is this:
Harmonicas being a mouth instrument, you'll find that certain makes and models seems to "fit" your mouth better than others, and the only way to find out what your preference is, is to buy and try them.
When you are an absolute beginner it doesn't matter as much, because you are just getting used to the basics of how harmonica reeds respond, how to move about on the instrument, what the blow and draw holes sound like, etc.
Then when you start to get a little more advanced you start to try out different models according not just how they seem to "fit" but also how they seem to respond when you try a particular playing technique.
Once again, this takes experimentation and trying out different makes and models.
There actually are 12 basic keys of harmonicas you can buy, but your key of C is a good start.
The key of C is a midrange harmonica – not high, not low, and it is the harmonica used in almost all the instructional packages you could buy.
If you are going to be playing a lot of blues, the A harp will come in real handy, because so much blues is in the key of E - and the key of A harmonica is the 2nd position, "crossharp" for a song in the key of E.
What's a Chromatic harmonica?
These models incorporate the full chromatic scale and allow the player to play in any key using one harmonica. Chromatic models provide the complete 12 note octave with all sharps and flats. Each hole contains four reeds: two are for natural notes and two for chromatic notes. The reeds for chromatic notes are brought into operation by pushing a slide button on the side of the harmonica. This closes off the air flow from one set or reeds and permits the other set to vibrate freely. The preferred instrument for Jazz and Classical, chromatic harmonicas are also used for Blues and Popular Music. Here's more on Chromatic harmonicas
Which diatonic harmonica is the best?
Consider the most popular models among pros, such as (in no particular order) the Hohner Marine Band, Hohner Blues Harp, Lee Oskar Major Diatonic, Hering Blues, Hohner Golden Melody and Hohner Big River.