Answer:
The most effective way to invert sentence (6) in order to vary sentence patterns is Best of all are the days we go horseback riding.
Step-by-step explanation:
The original sentence "The days we go horseback riding are the best of all." can have a pattern variation by switching its speech elements without changing its meaning, this would be with the sentence "Best of all are the days we go horseback riding" where superlative becomes the noun of the sentence.