Which Option Greek Is Most Important for a Long Option Position to Overcome Theta?

Delta is the most important option Greek for a long option position to overcome Theta. Delta measures the change in option price for a $1 change in the underlying asset.

For a long option to be profitable, the gain from the favorable price movement (Delta profit) must exceed the loss from time decay (Theta loss). Therefore, a high Delta and a strong, quick move in the underlying are essential.