By economy you mean fuel avg right?
If so, then as per many members and owners here, they are getting 17-20 km/ltr in their altos and cultuses....wagonR may be slightly low like in 14-17 range but i have taken all the 3 cars as a whole..
U cant compare these cars on their exact fuel avg figures because company claims something and owners get other...the owners are themselves so much mixed like for eg my cousin with heavy foot was getting max 11 on his WagonR, next month with same car and light foot i got round 15.
This is why i have taken all 3 in same bracket
U see both cultus and WagonR have same engine, while its pretty obvious that people with alto are getting atleast 15plus avgs