Lemme first tell you what are the pros and cons of each.
Tata Indigo Manza is a complete package. Great looks, more finished and by looks it definitely is a Sedan. On the other hand, I tag Dzire as the one of the ugliest cars on road and it does not even qualify to be a Sedan. Tata Indigo Manza is more spacious than SWift Dzire. Manza's pickup is better than that of Swift. Indigo Manza uses the same engine which powers Punto and we all know Fiat's technology for the real performance. Manza's AC scores over Dzire.
On the other hand, Swift Dzire has good resale value. Well, we do not know of Manza yet. Maruti is know for better customer satisfaction than Tata.
In my personal opinion, I would always go for Tata Indigo Manza if I ever have to choose between them.