One store sells milk for $3.00 per gallon. A second store sells milk for $0.80 per quart. Which is best?

Two pints in a quart, four quarts in a gallon.  You work it out!

Depends on whether you prefer the gallon it in one bottle or four bottles.

Whichever one is most convenient for you is usually the one that you buy.

Or you can decide which to buy on the lowest cost per ounce.

"Best" is not an obvious criterion.