I am myself about to buy a car in this segement. I have taken test drives for Santro, Zen, Tata Indica (Petrol), Tata Indica (Diesel) and have talked to numerous people who own these vehicles. I have come to the following conclusion:
Unless you have atleast 100 Km per day avarage of running of your car, do not buy Diesel based car.
Santro (with power steering) was best in terms of engine noise, pickup, A/C and cofortable drive experience.
Tata Indica Petrol was also good in terms of pickup, but the salesman told me that if I want to go for petrol engine I should better go for either Zen or Santro. Tatas strength is in diesel engine. Somehow, inspite of the better claimed BHP in Tata Indica Petrol, I felt that the pick up of santro was still better and so is the A/C.
I currently own a Maruti 800 and am very much uncomfortable everytime I have to get in or get out of my car. Its height is too small. Zen and Indica both have same issue.
Somehow I found that engine noise while driving is more in Zen as compared to Santro.
Overall I have rated the cars in following order
Santro (with power steering)
Tata Indica (Diesel) because of its fuel economy.
Zen
Tata Indica (Petrol)
Regarding fuel efficiency feedback to me has been as follows
Tata Indica (Diesel)
Zen
Tata Indica (Petro)/ Santro
I hope you found the above useful.
Cheers.