Go for Michelin Energy XM2 or Bridgestone Turanza AR20 tyres for your Santro. Turanza would be a better option if your usage will be over rough or unpaved roads as they are more durable than Michelin. Both these tyres have long tread life.
However, if you want an economical option then go for MRF ZVTV. It offers decent performance and has long tyre life, but is a little noisy at high speeds.