Given the limited running you are doing, most of it on the highway, the Tata Sierra with the 1.5 TGDI and 6-speed AT is a better option than the Seltos 1.5 NA with the IVT or CVT transmission.
The Seltos is a good car, no doubt, and more soundly engineered than the Sierra, but what we like about the Sierra is the powertrain, which is punchy, refined and has smooth gear shifts. Whilst the Seltos 1.5 with the CVT would be great in the city and in stop-and-go traffic, the CVT’s ‘rubber band’ effect would make the engine sound a bit loud or strained at high speeds.