Which one is better the air cooler or the air conditioner?

In the humid warm climate an air conditioner is the solution. In dry hot climate and air cooler (aka evaporative cooler) works best since it cools by evaporation of water and introduces a lot of humidity in the space. An air cooler is not usually recommended (even in dry climate) for rooms where electrical/electronic equipments (such as TV, PC etc) are placed since too much humidity mixed with already deposited dust makes a mess and results in failure.

Also air cooler is cheaper in cost as well as operation.