Both the Kia Seltos and Sonet diesels are competent and enjoyable, but with your usage of around 7,000km a year, a diesel simply doesn’t make financial or mechanical sense. The higher upfront cost of the diesel will take a long time to recover at that mileage, and you also won’t be using the engine in the way modern diesels are designed for. A key concern is the DPF (diesel particulate filter). This sits in the exhaust and traps soot; every so often, it needs to get hot enough to burn that soot off in a process called regeneration. This typically happens when the car is driven for a sustained period at higher speeds and with the exhaust fully up to temperature. If your running is mostly short, low-speed trips, the DPF may not regenerate properly, leading to soot build-up, warning lights, reduced performance and, in the worst case, an expensive repair or replacement.
Given your usage, a petrol car makes far more sense. The 1.0 turbo-petrol with the 7-speed DCT gives you a strong mid-range punch that feels very close to a diesel in everyday driving, but without the DPF worries. It is smooth, refined and well suited to mixed city and highway use. Between the Kia Sonet and Seltos, the Sonet is the better fit if you usually drive alone or with just one passenger; it’s more compact, easier to park and generally costs less to buy like-for-like. The Seltos is the one to pick if you regularly travel with family, thanks to its extra space, bigger boot and more “proper SUV” feel, though some variants are noticeably pricier. 
