The KTM 250 Duke you are considering makes for a great one-bike garage to handle city and highway duties both. It has a punchy – yet not overwhelming – amount of grunt, engaging handling and will also return good fuel economy.
Coming to the Triumph Speed T4, depending on how you ride, you should see decent fuel economy even inside city traffic. Since the bike is made by Bajaj, it shouldn’t be too expensive to maintain. The advantage of the Speed T4 over the Duke will be its more effortless performance and more comfortable seating and suspension.
And since you are shopping in this space, the TVS Apache RTR 310 is also worth taking a look at. The RTR 310 is a feature-rich machine with good performance and handling. Also, we will recommend you get the variant with the quickshifter as it is still priced sensibly, and this feature will enhance the riding experience.
Since these are different machines in the riding experience they deliver, we’d recommend a test ride of all three before you decide.