Two systems stacked together
Your blood type is really two separate traits combined: the ABO group (O, A, B, or AB) and the Rh factor (positive or negative) — giving the 8 types you'll see on donor cards and hospital request forms.
In most populations, O and A are the most common ABO groups and AB is the least common. Rh-negative is a minority trait in every population studied — nowhere is it the majority.
Why "rare" depends on where you live
Rh-negative types are notably less common in Middle Eastern and Asian populations than in populations of European descent. That's part of why O- gets singled out as rare and highly requested: it combines a minority Rh status with being the universal donor, compatible with all 8 types — valuable exactly because it's both useful and scarce.
AB- combines the least common ABO group with Rh-negative status, and is typically the rarest single combination in populations studied.
Check your own type
Every blood type has its own compatibility page with a full donor/recipient breakdown — start from the blood type guide to find yours.