Decorated griffin and preventing damage

[Paraluke]

 {Decorated Griffin} has the ability to prevent damage. Say if I have {Spear of Heliod} in play and I have 2 1/1s attacking me. Assuming I activated griffin's ability once and I am not blocking any of the 1/1s.

Since combat damage is simultaneous, how would I know which 1/1's damage is prevented and which creature I could destroy with the spear, since dealing 0 damage is not considered as dealt damage?

[Keyeto]

You get to choose, since you are the "shielded" player:

615.7.: Some prevention effects generated by the resolution of a spell or ability refer to a specific amount of damage -- for example, "Prevent the next 3 damage that would be dealt to target creature or player this turn." These work like shields. Each 1 damage that would be dealt to the "shielded" creature or player is prevented. Preventing 1 damage reduces the remaining shield by 1. If damage would be dealt to the shielded creature or player by two or more applicable sources at the same time, the player or the controller of the creature chooses which damage the shield prevents. Once the shield has been reduced to 0, any remaining damage is dealt normally. Such effects count only the amount of damage; the number of events or sources dealing it doesn't matter.

[Paraluke]

Oh man I need to read more rules. Thanks again keyeto.