The cars you have shortlisted are very different, but based on your usage and your mileage requirement, we would suggest going for the Kia Seltos with the 1.5 litre naturally aspirated engine paired to the IVT automatic.

The new Seltos has grown in size compared to the previous generation, which not only improves interior space, comfort and boot capacity, but also gives it better road presence. While it lacks outright punch, for most real world conditions and sedate driving it has more than enough performance, both in the city and on the highway. The biggest strength of this powertrain is its refinement and smoothness, which makes the Seltos a pleasure to drive, especially in urban conditions. In terms of mileage, the Seltos with this engine and gearbox should come close to your requirement of 12 kmpl or more, something the other two cars are unlikely to achieve. You can get the HTK(O) variant in your budget which is well loaded with features too.

The Tata Harrier petrol, on the other hand, is larger and has more presence, but it is also more expensive. In fact, the Harrier turbo petrol with the 6 speed automatic costs over Rs 20 lakh on road, which is more than Rs 2 lakh over your budget. Fuel efficiency will also be lower than the Kia’s, as the Harrier is heavier, more powerful, and turbo petrol engines are generally more sensitive to throttle inputs.

This issue is even more pronounced in the Mahindra Scorpio N. It is the heaviest car here, uses a large turbo petrol engine producing over 200 PS, and while it delivers effortless performance, efficiency takes a hit. Being based on a ladder frame chassis, it is more rugged, but for everyday use it won’t be as comfortable as the other two. If you want to buy a Mahindra, we would suggest looking at the new 7XO instead, as it is more practical, more comfortable, and will also be more fuel efficient.

Since you are able to purchase a new Kia Seltos or Carens Clavis EV, we would suggest you not look at a used Tata Harrier or XUV700, as these are quite close in size, performance and features. If you are buying used, it makes sense to get something from two segments above. 

As to your query about a diesel or electric, yes, both are not likely to have a high resale value. There's certainly a cloud over diesel's long term future, and the pre-owned EV market is too nascent to judge future potential. 

We would, however, recommend the EV as you will be keeping your car for about 10 years, and in that time with your running you would save on fuel bills. Between the Hyundai Creta electric and the Clavis EV, we would suggest the Kia as it's very similar mechanically. But also offers you the benefit of the third row of seats, which is quite spacious and usable. 

While there are a lot of SUV options that fall within your budget, we've listed the top models worth checking out. Among the monocoque-bodied SUV options, there's Tata's Harrier and Safari, and the Mahindra XUV 7XO. These SUVs are large and have great road presence. Also, being monocoque SUVs, they score well on comfort and refinement. 
 

If you are looking for something more hardcore, there's the option of Mahindra's ladder frame SUVs, namely the Scorpio N and Thar Roxx. These SUVs are big on image and have a toughness about them that's very appealing. 

However, they are not as comfortable as the models listed above. 

A very Happy New Year to you too! 

Both the Tata and Mahindra cars are excellent choices, but of the two, we'd recommend waiting for the Mahindra XUV 7XO, whose launch is right around the corner. It will have a more modern interior and likely more features too, and going by its predecessor, the XUV 700. 

It will also have the more refined diesel engine and slicker manual gearbox. We will say the Tata Safari has the edge on space, especially in the third row, and its ride quality is slightly more comfortable. Plus, there will likely be a long waiting period for the Mahindra XUV 7XO once it is launched. 

So, if you are in a hurry, the Tata might be easier to get sooner. But in most other areas, the Mahindra comes out on top. Another consideration, especially for your elderly family members, is that ingress and egress to the cabin are slightly easier in the Mahindra than the Tata.