Cutting the grass can be considered either a chore or a treat, depending on your perspective.
While price is always a consideration, you ultimately choose a gas-powered lawn mower based on the amount of energy you want expend mowing.
There are basically two types of gas-powered lawn mowers: push and self-propelled.
Push Lawn Mowers

The name says it all. To power a
push lawn mower, you do just that... push it.
The engine on a push mower is designed to cut thick grass, but it doesn't propel the lawn mower forward.
You'll be providing the "horsepower" to move these mowers, and you're going to break a sweat.
If you have a yard with lots of inclines or hills, you shouldn't use a push mower unless you're in good physical condition.
Self-Propelled Lawn Mowers
Self-Propelled lawn mowers are very easy to operate and maneuver. You won't be supplying the power to move these mowers, you'll just be steering them.
Self-propelled mowers work well on hills because you won't have to break your back powering them around your lawn. They work well on all types of terrain and are easy to maneuver around obstacles.