For around 1,000km of monthly running, a petrol SUV would suit your needs well. Since nearly 80% of your driving is within the city, an automatic will be far more convenient than a manual.
The Kia Seltos is the largest and most spacious SUV in this comparison, while the Nexon and Venue are both sub-four-metre SUVs. The Seltos HTK (O) variant is a tempting option, but it misses out on a few features you might expect at this price point. Automatic climate control, a 360-degree camera and ventilated seats are not offered. Also, the 1.5-litre petrol engine feels a bit underpowered compared to the 1.0-litre turbo-petrol available on the Venue HX 8, which fits within the same budget.
The Venue also offers a stronger feature set overall and if value for money is important to you, it is the better buy.
The Nexon CNG fits within the budget and will be the cheapest to run. However, you will have to deal with long waiting times at CNG stations, especially in the city where most of your driving will be.
If you want a spacious SUV with a smooth driving experience, the Kia Seltos HTK (O) with the CVT gearbox is a good choice. But if you want the maximum number of features and are willing to compromise slightly on rear seat space, the Venue is the one to go for. The Nexon is worth considering only if fuel efficiency is your top priority.