Maruti Suzuki Brezza

Given that your usage is relatively high and mainly on the highway, you should go for the Kia Sonet diesel MT. Its strong pulling power compared to the naturally aspirated petrol engines you have mentioned will allow for more effortless cruising and overtaking, and the fuel efficiency will be considerably better too. 

You should also consider the new Hyundai Venue, as it is a bit more modern and more spacious than the Sonet. As for the fuel economy of the petrol engines, it depends on your driving style and conditions. Since your driving is mainly on the highway, the larger, more powerful 1.5-litre petrol in the Maruti Suzuki Brezza would likely be more efficient on the whole, as it would be less strained at higher speeds than the Sonet's 1.2 petrol.

Given that you are looking at an upgrade from a compact SUV like the Maruti Suzuki Brezza, it would be worthwhile looking at the larger mid-size SUV segment. 

However, bear in mind, then, that you would likely have to stretch your budget a bit to get a good amount of features. We would advise holding off on your purchase for a little longer if possible, as there are several exciting new cars launching very soon. 

First is the Tata Sierra, a good-looking and well-equipped SUV whose full price list is expected later this month. Then there is the all-new Kia Seltos, which promises to be larger and even better equipped than today's car.

 And finally is the new Renault Duster, which promises the same robust SUV feel and value proposition as the original, with more modern features. All should be big on safety, although official crash test ratings remain to be seen.

Since you prefer a low service cost and an easy-on-the-pocket car, it would be better to stick to Maruti Suzuki as a brand. 

Maruti is renowned for low service and running costs and will offer peace of mind, just like the Maruti Celerio has. If you want a bigger car in particular, the Maruti Suzuki Brezza is a good option to consider. It has a roomy cabin, a comfy ride, the automatic is convenient for the city, and the running costs are low, too. 

Also, it has a good boot space and holds its value well. The other, more compact option would be the Maruti Suzuki Fronx with a turbo-petrol engine and a 6-speed automatic gearbox. It isn't as big as the Brezza, but it is very nice to drive and quite practical too. Both cars in their top-spec variants will fit in your budget. 

Given your requirements, you should choose between the Maruti Suzuki Brezza and the Maruti Suzuki Fronx. 

Both models come with petrol engines mated to a torque converter automatic gearbox, and being a Maruti car, you know they will be reliable and fuss-free to live with. 

The Brezza gets a 103hp, 136Nm, 1.5-litre naturally aspirated engine, and it has more interior space and features than the Fronx. The Fronx, meanwhile, gets a punchier 100hp, 147Nm, 1.0-litre turbo-petrol engine, and it comes across as the better-looking model of the two thanks to its coupe-SUV-like design. 

In terms of fuel efficiency, the Brezza's naturally aspirated engine should be more efficient than the Fronx's turbo on your daily city commutes.