Emphasizing promptness:
* Alacrity: This is the most common word for promptness with a sense of eagerness.
* Readiness: This emphasizes being prepared and quick to act.
* Promptness: This is straightforward and simply means acting without delay.
Emphasizing cheerful willingness:
* Eagerness: This implies enthusiasm and anticipation.
* Enthusiasm: This highlights strong positive feelings.
* Zeal: This suggests passionate commitment and energy.
Combining both elements:
* Gusto: This implies enjoyment and energetic willingness.
* Vivacity: This emphasizes a lively and enthusiastic spirit.
* Heartiness: This suggests a warm and friendly willingness.
The best word will depend on the specific context and the tone you want to convey.