A new bike will come with a warranty, and you will be the first one to break it in, so the peace of mind of buying a new machine is not to be discounted. 

If you are looking at older bikes that are 4-5 years old or more, then you will also need to budget for a comprehensive service and perhaps some replacement cycle parts like tyres and brakes. 

While the KTM 390 Duke is a great option, you could also look at the Royal Enfield Guerrilla 450 since you've already owned a bike from the same brand. 

Of the three bikes you have shortlisted, we would suggest you choose between the Triumph Speed T4 and the Royal Enfield Scram 440. These two will be more comfortable, although the Royal Enfield Guerrilla will give you more performance on the highway. 

Since you've already owned a Royal Enfield Classic, the latest Royal Enfield Bullet / Classic is also worth taking a good look at because they will offer you good comfort and ride quality - both of which are important to you. 

You can alternatively also look at the Honda CB350 models because they are comfortable, smooth, well-built and torquey. 

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

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. 

Among the bikes you have shortlisted, we'd recommend choosing between the RE Guerrilla 450 or the Honda CB350RS. The Guerrilla is better suited for highway rides, thanks to its more powerful engine. On the other hand, the CB350RS makes a great city bike with its light clutch and smooth, torquey motor.

In a similar price range, the RE Scram 440 is also worth considering. It can comfortably cruise at 100-110 km/h on highways and offers good suspension comfort for broken city roads.

If you’re open to stretching your budget a little, the RE Himalayan 450 is another strong contender. It’s a wonderful highway tourer and still quite manageable for city use.

The Triumph Speed 400 is built entirely by Bajaj, which means its spare parts are easy to find and light on the pocket. 

We’d also suggest checking out the Royal Enfield Guerrilla 450. It offers similar performance and running costs, and you might find it a great fit for your riding style too.