Since mileage is important to you, we would suggest the Hyundai Venue. We have yet to put the new generation car through our standard fuel efficiency test cycle. 

However, given that it carries over its powertrains, we expect it to perform better than the Mahindra XUV 3XO. The Mahindra car is tuned more for a peppy throttle response, and this drops its real-world fuel efficiency. 

You're right, the Renault Kiger is a modern car which is decently equipped, but its resale value isn't as strong as some other options in this segment. The Kia Sonet feels more polished overall, and it will get you more features too. 

Yes, the iMT is convenient, but try getting a proper automatic instead, which will be a far more convenient and smoother option. If you want something a bit more modern, the Hyundai Venue is also an option you must consider. The Mahindra XUV3XO is also a compact SUV you may consider.
 

Given your positive experience with the Mahindra car, upgrading to an XUV 3XO would be a good choice. It has a powerful diesel engine that is responsive and refined. It has all the latest safety kit with a 5-star safety rating by Bharat NCAP, and with a diesel engine, it offers low running costs as well. 

The ride comfort is also positive, and it holds its own very well on bad roads. In your budget, you can get the AX7 trim that gets a well-equipped cabin with the necessary features. 

A good option to also look at would be the newly unveiled Kia Seltos. It is a new generation model with a lot of changes, an upmarket cabin and even more features added. Kia has also retained the powertrain options so should you want a diesel, you can get that as well. 

If you want a bigger SUV, the Mahindra XUV 700 will also be updated to the Mahindra XUV 7XO with a refreshed look and new features in January. 

Although it is worth noting that the XUV will be pushing the Rs 25 lakh mark in terms of price. The Renault Duster is also an iconic model that is set to make a comeback next month so it is definitely worth waiting for. 

We would recommend the new Hyundai Venue as it is a very good all-rounder, and you will get a well-equipped variant too. 

Pick from the naturally aspirated petrol models as the turbo petrol engine is very sensitive to driving style, and its real-world efficiency is often well lower than the claimed figure. 

The Mahindra 3XO is also a good all-rounder; however, it's geared more towards a peppy drive experience, and this comes at the expense of fuel efficiency, and since which is important for you, so it's best avoided.