O+ is the most common one but it can only donate to other positives (75% of the population). O- is the universal donor. A- is actually the third most valuable type because it can be given to all the As and ABs, with A+ being the second most common.
Blood Type: Distribution (Population Covered by Blood Type)(Population That Can Cover That Blood Type)
- O positive: 35% (75%) (48%)
- O negative: 13% (100%) (13%)
- A positive: 30% (32%) (86%)
- A negative: 8% (40%) (21%)
- B positive: 8% (10%) (23%)
- B negative: 2% (13%) (15%)
- AB positive: 2% (2%) (100%)
- AB negative: 1% (3%) (24%)
In conclusion:
AB+ are leeches