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. 

Stepping up from 20hp to 130hp in a single shot doesn't seem like the safest upgrade. We would like to recommend that you upgrade to something more approachable, like the KTM 390 Duke seems like a more sensible option. If you still want a multi-cylinder bike, something like the Kawasaki 650 and the Honda 650, as well as the CB750 Hornet will be more manageable. 

Try and take a test ride of everything you're considering before you put your money down. 

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. 

The Triumph Speed 400 is ideal for city riding needs, thanks to its smooth, tractable engine. It is lightweight, easily manageable in traffic, and also the most affordable option from this lot of motorcycles. The KTM 390 Duke offers more aggressive performance, sharper handling and has more features, but the ride quality is on the stiffer side to keep in tune with its sporty nature. 

The Kawasaki Ninja 300, the only twin-cylinder motorcycle on your list, has been around for a long time and hasn't received any modern updates. The cost of servicing and spare parts of Kawasaki is also on the higher side. We still suggest you take a test ride of all three bikes to see which one suits you best.

If you want your new bike to be sporty and compact, then bikes like the KTM 390 Duke, TVS Apache RTR 310 and Honda CB300R would be our recommendation. 

If you want to have a machine that's capable of doing longer distances with luggage and/or a pillion, then an adventure bike like the KTM 390 Adventure (either of the 2 variants will do) or the Royal Enfield Himalayan 450 will fit the bill. 

Before pulling the trigger, try to get long test rides of every bike you are considering to make an informed decision.