The Maruti Suzuki Brezza’s 1.5-litre engine is known to deliver good fuel economy and also offers more power and performance than the 1.2-litre unit on the Kia Sonet. The Brezza will be the better petrol option for you. The Sonet diesel will be more efficient than the Brezza, but your running of 1000-1200km a month doesn’t justify the extra spend on a diesel. Also, modern BS6 diesels need extra care with a long drive every couple of days to help the diesel particulate filter (DPF) regenerate. Failure to do so can cause engine trouble.
We’d suggest you go for the Brezza, which will be a hassle-free option for your needs.