Gas vs Electric vs unpowered mowers

Gas mowers
Pros

Lots of power, should cut tall or wet grass easier than other options

Versatile - no need to find an outlet

Cons

Need to keep gasoline on hand

Yearly oil and air filter changes

Much harder to start than other options

Get this if: You want to impress the neighbors with the sheer power, or you are a contract gardner and need to work quickly without a battery or cord.

Push reel mowers
Pros

Human powered, the most green option

Get more excercise while you mow

Almost maintenance free

Cons

Does not do well with tall or wet grass

Narrower cut width than other options

Mowing will take more time than with a powered mower

Get this if: You have a small lawn and will mow it frequently, or if mowing the lawn is your weekly workout.

Corded Electric Mowers
Pros

Almost maintenance free

Almost as much power as gas

Lightweight

Cons

Does not do well with tall or wet grass

Cord management can be an issue; depending on your lawn layout

Get this if: You want the speed of a powered mower without the maintenance or weight of gas and your lawn is relatively simple (not too many trees in the middle)

Battery Electric Mowers
Pros

Powered but without gas or a cord

Cons

Does not do well with tall or wet grass

Battery has a limited charge capacity (best for small lawns)

Heavier than most other options

Battery will need to be replaced after a few years

Get this if: You have a small lawn, really want an electric mower, and a corded model won't work for you.