When it comes to power, pellet guns vs BB guns can vary drastically. Generally, pellet airguns are more powerful than BB airguns. Pellet guns typically fire heavier pellets and have higher muzzle velocities. However, the power of the gun depends more on the powerplant than the ammunition. In order from most to least powerful; PCP, Spring/Gas Piston, pump pneumatic, and CO2.
When you're looking for accuracy, pellet guns are generally more accurate than BB guns. This is because pellet guns typically have rifled barrels that provide a spin to the pellets as they travel through the barrel, improving accuracy and range. BB guns, on the other hand, tend to have smoothbore barrels that don't spin the ammunition.
Ultimately, when you're considering power and accuracy, pellet guns are a better option than BB guns. However, when power and accuracy aren't an issue, BB guns are an excellent choice.