KTM 250 Duke Gen 3

Of the three bikes you're considering, the KTM 250 Duke will be the most engaging handler, but it has the least peak output and the smallest engine. This means you will have to rev it more to access the meat of the performance.

The Triumph Speed 400 is the most powerful bike of your shortlisted options. It will be a great city bike because of its effortless performance and plush suspension.

The TVS Apache RTX 300 is sure to be the most comfortable machine of the three. Its long-travel suspension and commanding ergonomics help, but it is also the tallest and heaviest bike on your list.

Take a test ride of all three to see which one fits your needs the best.

If you are comfortable with the size and heft of the TVS Apache RTX 300, then it is certainly worth considering because it will fit your needs quite well. 

If you want something in the same price range that is lighter and more manageable, then bikes like the Bajaj Pulsar NS400Z and the KTM 250 Duke are worth considering. 

Take exhaustive test rides of all the machines you shortlist before you decide. 

Given that you want something manageable and this will be your first bike, here are a few options we recommend.

The Honda CB300F and CB300R are both lightweight, well-built, and have low seat heights. You could also check out the KTM 250 Duke or the Husqvarna Vitpilen 250. Both are mechanically identical, but they differ in styling and riding posture, the Vitpilen has a slightly taller seat than the Duke.

All these are fun and entertaining first bike with a reasonable performance ceiling to keep you interested for a long time.