If you are buying a petrol automatic, the Tata Sierra makes more sense if mileage, features and lower running costs are your priority. Its smaller 1.5 litre turbo petrol engine and overall size should make it more efficient. You also get a more feature-rich cabin at a lower price, as the two sit in different segments.
The Mahindra XUV 7XO suits buyers who want a more traditional SUV feel with stronger road presence and a proven mechanical package. Its powerful 2.0-litre turbo petrol engine delivers more effortless performance. But the petrol automatic will be less efficient and costlier to run. If long term reliability and established credentials matter more, the XUV 7XO is the safer bet.