There is no second doubt about that in my mind. When people would be getting a car that is as equipped to handle the Indian roads as the Maruti 800 with probably more seating space inside & that too at nearly half the price, then only a fanatic Maruti lover will go buy the 800, no1 else!!
The Nano any day sports a more fuel efficient engine that will churn out great mileage figures of around 20-22 km/l in the city. That would also go in its favour because people buying a car in this bracket will definitely be very concerned about their petrol bills for sure.