Tata Nexon

First, a small correction. The Mahindra XUV 3XO does not use an AMT gearbox. It comes with a proper torque converter automatic, which offers a much smoother and more refined driving experience compared to AMTs. This makes it easier to drive in city traffic and overall more comfortable for daily use.

Because of this, the XUV 3XO MX2 Pro automatic becomes the better choice between the two cars you shortlisted. The wider cabin also makes it more comfortable for a family of five and the ride quality is well suited for both city drives and occasional highway trips.

The Tata Nexon does offer a DCA/DCT automatic option with the turbo-petrol engine, but that variant is significantly more expensive and would go well beyond your ₹11–12 lakh budget. The Nexon AMT variants therefore do not match the smoothness of the torque converter automatic offered in the 3XO.

For your requirements of ease of driving, comfort and a better automatic gearbox, the Mahindra XUV 3XO automatic would be the better option over the Nexon in your budget.

The Hyundai Venue will feel like a big upgrade from your Hyundai Santro AMT. The turbo petrol engine paired with the DCT gearbox offers strong performance and smooth shifts, which makes driving in the city effortless. It also gets features like a reverse camera, Android Auto connectivity and voice commands that you are specifically looking for. Overall, it will be a noticeable step up in terms of power, features, space and overall comfort.

Among the other cars you mentioned, the Kia Sonet is also a good option. However, the Venue is the newer car and is more spacious. Also, a replacement for the Sonet is expected next year, which means it may feel dated sooner. 

The Tata Nexon petrol is another option that offers good space and a comfortable ride, but the Venue feels more refined and easier to drive and is the newer car as well. 

As for the Kia Seltos, it is a good SUV, but it belongs to a higher segment and will stretch well beyond your ₹12-13 lakh budget in comparable variants.

With your daily running of around 50-60 km, your monthly usage will easily cross 1,500 km, so choosing a fuel with low running costs makes sense. In this case, CNG is generally a better fit than diesel, especially since most of your driving is in the city.

One of the better options to consider is the Tata Nexon CNG. Unlike most CNG cars, the Nexon uses a turbo-petrol engine, which means it still feels reasonably strong and comfortable even on the highway. The turbo engine produces good torque, which helps maintain performance despite running on CNG. This makes the Nexon CNG a good balance between low running costs for the city and decent highway performance for weekend drives.

Another practical option is the Maruti Suzuki Brezza CNG, particularly the LXi or VXi variants. The Brezza uses a 1.5-litre engine with factory-fitted CNG. It is known for being smooth and reliable while still offering good mileage and reasonable performance.

While the Tata Nexon has its strengths in a tough build and good suspension, its AMT gearbox is no match for the torque converter automatic. It comes paired with the Hyundai Venue and Kia Sonet's 1.5-litre diesel engine. The Hyundai and Kia's smooth diesel engines and slick auto gearboxes deliver a very polished driving experience, which you will love. 

Of the two, the Hyundai Venue is newer, offers more rear seat space and a few more frills like a larger 10.25-inch touchscreen. You'd get a Venue diesel-auto HX5 in your budget, which is reasonably well equipped and also packs in a sunroof. We can't recommend it wholeheartedly, though, because it misses the safety of a rear wiper. 

If rear seat space isn't a deal breaker and you are comfortable with the idea of buying a car that will be replaced in the near future, the Sonet diesel-auto HTX is definitely worth a look. 

For not much money over the Venue HX5, it packs in a whole lot more equipment such as LED headlights, push button start, leatherette seats and front seat ventilation. Also, it has the safety of a rear wiper, rear disc brakes and front parking sensors.  

After the EV, the turbo-petrol-DCA is the second-best iteration in the Nexon range. The drive experience is smooth and gearbox is seamless, although it is not the most refined in the segment. Of course, being a sub-4-metre car, manoeuvring it in town or parking in tight spots will be easier than a Sierra, and like you've mentioned, opting for an automatic comes with added convenience. Tata has done well to update the Nexon's interiors with modern features and tech, so even though it is an old platform, it is still up-to-speed with times. If you like the Nexon DCA, go for it - it'll be a good upgrade from your outgoing Maruti Ritz.

While you can do an aftermarket fitment of a CNG tank and system to a lot of cars, you are better off getting a factory-fitted system in the long run. Being designed, calibrated and tested in-house by the manufacturer means it will deliver optimal performance and efficiency and will be easier to maintain under warranty. The Tata Nexon iCNG is an excellent option for a number of different reasons. For one, its under-floor dual CNG tank design means you get a usable boot. It will not be the case in any aftermarket option, where the CNG tank will take up most of your boot space. 

The Nexon also has a powerful 1.2-litre turbocharged engine, which means it still has decent performance, even when running on CNG, which will be helpful for your highway-focused usage, while still delivering good mileage. And finally, Tata Motors offers a wide variety of trim levels even for its CNG offerings, and the Creative+ PS variant is pretty well kitted out.