Hi.. The basic difference between all of these variants of Maruti Alto is the safety and comfort features. The base model (Alto Std.) of Maruti Alto features stylish front bumper and grille, molded carpet, luggage compartment, electronic trip meter, integrated front seats, etc. The Alto Lx is the upgraded version of Maruti Alto and features rotary control of AC, tinted glasses, ac with heater, floor front console with cup holders, etc. The Alto Lxi is the fully loaded version which comes equipped with some additional new generation features like integrated rear seat head restraints, remote fuel lid opener, electronic power steering, fabric seats, etc..
However, all of these variants have been powered with a 796 cc petrol engine and offer an impressive mileage of 15.9 kmpl on city roads and 23.2 kmpl on highways. Thanks,