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. 

The TVS Apache RTR 310 will be a good step up from your current Apache RTR 180. The RTR 310 is a sporty machine with good performance and handling, which doesn't feel overly stiff or uncompromising and makes for a good all-rounder. 

As you have pointed out, there have been sporadic issues with TVS' aftersales. But if you are prepared to deal with them - and it does seem like your heart is set on the Apache - then you can go ahead with the RTR 310.

If you are open to looking at other brands, the Bajaj Pulsar NS400Z, Triumph Speed 400 and KTM 250 Duke all make for genuinely capable alternatives, with the Bajaj and Triumph also offering you quite a bit more performance. 

We would urge you to take a test ride and speak to your nearest dealer for aftersales of each bike so you can make a more informed decision. 

Some options you can consider are the TVS Apache RTR 310, KTM 390 Duke, Triumph Speed 400 and Royal Enfield Guerrilla 450. The Triumph and Royal Enfield aren't as overly sporty as the other two and will have a more effortless riding experience owing to their torque delivery, which is earlier in the rev band. 

The KTM 390 Duke is a proven product when it comes to sheer speed, but in its latest avatar has become quite compact, which may not be the best thing if you are a larger person. 

Last but not least, the TVS Apache RTR 310 has great handling and reasonable performance. We would recommend getting the variant with the quickshifter on the TVS as that offers the best value for your money. 

Take a test ride of everything you're considering before you decide. 

Both the bikes you have mentioned will fit the bill for your use case. However, both the Triumph Scrambler 400 X and the TVS Apache RTX 300 have tall seat heights (830mm or more), and for a new rider of your stature, they could feel like a little too much, especially at slow speeds and during off-roading. We would strongly recommend a test ride of both before you decide to go ahead with your purchase. 

If these two prove to be too tall for you, something more street-biased (and crucially, lower) like the Triumph Speed 400 or Apache RTR 310 from these respective brands would be a good fit. 

Among these two, the TVS Apache RR310 is the more modern and feature-packed motorcycle, making it more value for money. The Kawasaki Ninja 300 has not received any major updates in a long time and carries a higher price tag. The servicing and spare parts of Kawasaki will also be priced at a premium, so that is something to take into consideration. Two other bikes you can also check out are the KTM RC 390 and the Yamaha R3. Take test rides of all four bikes so you know which one suits you best.