Most Common Harps

These are the 7 harps I have in my travel case...

D = D, A & E (1st, 2nd & 3rd)
C = C, G & D
Bb = Bb, F & C
A = A, E & B
Ab = Ab, Eb & Bb (I love this harp for swing 3rd Position)
G = G, D & A
Low F = F, C & G (I prefer the Low F over the standard F)

12 Hole C Chromatic = All keys, but for me I play in 3rd Position, so it = D and Eb (slide-in)

As you can see, these 7 harps cover most of the keys (minus Db and Gb... very rare) with position knowledge.