MG Comet

Since your intended usage will be in Kolkata traffic, we don't recommend a diesel engine, like you have in your other two cars. Depending on your budget, you could consider a petrol car or even an EV. Among petrol cars, you could get a Maruti Swift under Rs 10 lakh, which is easygoing and efficient. And if you're after an EV, consider the MG Comet EV if you don't need a lot of space - its compact footprint makes it ideal for traffic. An EV will always have lower running costs and a smoother drive than a petrol car, which is helpful in traffic.

If you are open to buying an electric vehicle, the Tata Tiago EV is a good option for city use. It's got a smooth powertrain and is much more practical than the MG Comet you also considered. There's also the option of the Tata Punch EV, though it is slightly out of your budget. 

Among petrol automatic cars within your budget, the Hyundai i20 iVT and Citroen C3 AT have the smoothest automatic gearboxes. The Maruti Suzuki Swift AMT is also a good city car, though the AMT gearbox isn't as nice. 
 

The Tata Punch EV is a really well-rounded vehicle, and makes for a great EV runabout. However, if you are open to its unconventional styling and two-door layout, the MG Comet is an excellent secondary vehicle on account of its compact dimensions. It is very easy to drive and park, and it is one of those cars which you will truly appreciate for its merits as you begin to live with it.

Purely from a financial point of view, a petrol car will be a sensible option since the daily usage is limited. However, an EV like a MG Comet or Tata Tiago EV, will be far smoother and quieter than any ICE automatic option. So, get an EV only for the superior drive experience.