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. 

The new TVS Apache RTX 300 weighs nearly as much as your previous Dominar and is much taller than it, so if you are a shorter person, it may not be the best fit for you. It does have a wide handlebar and can make tight U-turns quite easily once you get used to its size, but that is a very subjective issue. 

Coming to the Apache RTR 310, that is a lighter and crucially, lower bike, and what we mean by that is that its centre of gravity is much lower, as is its seat height. This means that inside the city, it will be much more manageable, especially when making U-turns. Some other comparable bikes in this class are the KTM 250 Duke and the Triumph Speed 400, both have similiar performance and fuel economy to the Apache and are worth considering. 

If you aren't going to venture beyond 90kph on the highway and are primarily going to use the bike inside city limits, the Honda CB300F is a credible option to consider. It is a simpler and slower offering than the aforementioned bikes but has a very accessible 789mm seat height and a lithe 153kg kerb weight, which should make it very approachable. 

A test ride of these bikes will help you decide which is the best option for you. 

For your usage within your budget, you will have a good mix of neo-retro and sporty naked bikes to choose from. The Triumph Speed 400 and Royal Enfield Guerrilla 450 both combine minimalist, neo-retro design with 40hp performance. If you want something that's more relaxed, then look at options like the TVS Ronin, Honda CB350 models and the Royal Enfield Hunter 350. These are likely to be the most comfortable bikes of everything we'll recommend you try. 

If you want something a little sportier, then you should consider the TVS Apache RTR 310 and KTM 250 Duke / Husqvarna Svartpilen 250. These will feel more engaging and sporty than other bikes on the list while still being fairly usable and comfortable daily. 

Since all the bikes recommended here are very different, we'd recommend a thorough test ride to see which one suits you best. 

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.