Apparently both methods can achieve an efficacy rate in the mid-90s if done correctly. Pros and cons as I understand them:
Vaporizing is fast but requires a heating element and an energy source and fumes may not be healthy for the beekeeper. Dribbling only requires mixing OA (3.2% I think) in 1:1 sugar syrup and a large syringe but must be done while bees are clustered and broodless in cold weather and takes longer per hive. I have also heard the dribble method may be a little more harmful to the bees but that may have been due to inaccurate dosing.
FWIW, I have heard rumblings that the EPA is very close to officially approving OA for use in beehives. Apparently they will "hold the license" which precludes a commercial entity from having to pay a huge amount of money to get the approval. Although the folks I talked to weren't sure which method would be approved, they expected it would be the dribble method probably due to the danger of OA vapors.
Curious what folks experienced with these methods think about one vs. the other.