Riding mowers are more expensive, but offer many advantages to walk-behinds. The most obvious is that you are riding on it. If your lawn is 1/2 acre to 1 acre in size, you will want to consider a riding mower or a lawn tractor. More than 1 acre might take an even bigger tractor.
Riding mowers have a large deck size, referring to the size of the blade. A larger blade cuts more grass in one pass taking less time to cut the lawn, but also limits the places the mower can get to.
You will have to consider your landscaping to know if this is best for you. Riding lawn mowers can cost you $900 and up.