Each bike you are looking at offers a very different user experience, so we'll list each bike's pros and cons so you can make an informed decision. 

The Husqvarna Vitpilen 250 is a KTM 250 Duke that is wearing a neo-retro suit and as such will be comfortable, engaging yet not overwhelming to ride and return good fuel economy too. The downside is that finding a dealer could prove to be an issue depending on where you're located. 

The Honda CB350RS is the slowest bike among the four you've shortlisted, but it is a proven machine offering comfort, good fuel economy and the promise of reliability in the long run. 

The Royal Enfield Guerrilla 450 is the fastest, most powerful bike here and will feel the most lively to ride thanks to its punchy engine and eager handling. Its sporty - read: stiff - suspension setup may not be to everyone's tastes, however. 

Lastly, the Bajaj Dominar 400 is the oldest bike here, and also the heaviest, but it packs in a powerful KTM-sourced engine and for highway touring will feel the most adept. However, its heavy weight will mean more effort inside the city.

We'd recommend you take a thorough test ride of all these bikes before you make up your mind. 

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.