We have three lawn mowers. Here is my comparison of two of them –

Positives of a Gas-Powered (Rotary) Mower Over A Push (Reel) Mower:

It is self propelling
It is wider and covers more area
It mulches better
It mows more completely
It doesn’t get stuck on sticks

Positives of a Push Mower over a Gas-Powered Mower:

Much less expensive
Doesn’t require gas
Easier to start
Less likely to chop off a finger
If a kid can push it, he can run it
Good exercise
Makes almost no noise.

My recommendation: If you have a small yard, go for the push mower.