An AC. 1 ton could consume up to 1KW of electricity. It depends upon the rating, which you can see in the form of stars. A 3-star non-inverter AC may consume 1 unit within 1 hour. Try to pick a 5-star rating unit. It consumes much less power. A window AC usually consumes much more electricity than a split AC.
Dual Inverter AC is the best and economical AC. However, please note that lack of maintenance could lead to more consumption and increase your electricity bills.