Final answer:
The word that correctly completes the sentence is 'better'.
Step-by-step explanation:
The word that would correctly complete the sentence is better.
The word 'better' is the comparative form of the adjective 'good'. In this sentence, we are comparing today's lunch with yesterday's lunch. Since 'better' is the comparative form of 'good', it should be used to show that today's lunch is superior to yesterday's lunch.
For example: Today's lunch is better than yesterday's lunch.
Learn more about Comparative Adjectives