96-97% is top efficiency for any furnace.

Price goes up to achieve higher levels of comfort.

Best way to imagine this is to think of an above ground pool. Top few inches of water are warm, bottom is colder by a few degrees. Think of the water like your home, and the uneven temperatures throughout your home.

Single Stage furnaces are like If a big grown adult did 1 cannonball into the pool. They will mix up SOME of the water, but not all.

Two Stage furnaces Or, what if a medium size person did a few cannonballs, and would mix up the water even more.

Modulating Furnaces are like if we put several small children in the water for an hour. The water will be perfectly mixed when they get out.