Both bikes you have considered are good for a beginner rider. The Honda CB350 H'ness will feel like a more spacious and larger machine than the Hunter, which will be a good thing if you are a larger rider. 

On the flip side, with its smaller size and 17-inch wheels, the Royal Enfield Hunter 350 will feel more agile and flickable in city traffic. Do bear in mind that coming from an Activa, both these bikes will feel quite heavy, weighing 181kg.

Something that will be similar to a ride but substantially lighter will be the TVS Ronin, which weighs 160kg. We recommend you take a look at the Ronin instead of the two 350s. Even though you are familiar with how to operate a clutch and change gears in a car, on a motorcycle, it is a different ballgame. 

Do take a test ride of the machines you shortlist before you decide. 

Since you already own a Unicorn, stepping up to the Honda CB350RS is a logical move. The CB350RS is a reasonably comfortable machine with a smooth engine and should offer you more riding comfort and enjoyment than your Unicorn. That being said, it is worth checking out its siblings - the base CB350 and the CB350 H'ness - because all three, while mechanically very similar, have different riding positions and price points. We would recommend getting the one that you find the most comfortable on account of your long daily commute.

Other options also worth taking a look at are the TVS Ronin and the Royal Enfield Hunter / Classic / Bullet 350. These are comfortable, reasonably fuel-efficient and reliable bikes which will be a good fit for you. 

A test ride of these will help you figure out which is the best option for you. 

The Honda CB350 and CB350 H'ness are essentially the same bike wearing different outfits. The former mimics the design language of the popular Royal Enfield 350s, while the latter has a distinct Honda design. 

As such, their riding experiences are going to be exceedingly similar and picking between the two will come down to which one you prefer the look of. 

Coming to your query, both these bikes offer good pillion comfort and are good to ride in dense city traffic with their neutral handling and light clutch action, thanks to the slip/assist clutch. 

All the bikes you are considering are great options and have reasonable servicing costs. The CB350 H'ness is a relaxed, comfortable retro bike with a smooth, torquey engine. The Honda NX200 is a tall, quasi-ADV based on the Hornet 2.0 street bike, which means it will be suitable for daily use. 

The Gixxer and V-Strom SX from Suzuki are refined, punchy machines that are also fuel-efficient and quite reliable. 

A test ride of all 4 is in order so that you can decide which is the best option for your needs. 

All bikes you have shortlisted make for good beginner bikes with their unique strengths. The Yamaha XSR155 / MT-15 will be the lightest and easiest to manage machines with a sporty and engaging engine + chassis combination. They will also return excellent fuel economy. However, over long stretches of bad roads, the stiff suspension will cause some discomfort.

The Honda CB350 H'ness and Royal Enfield Hunter 350 are laid-back roadsters with torquey, smooth 350cc engines. They will be more comfortable but will not have as good fuel economy or handling capabilities. 

It all boils down to the sort of experience you are after and the design you like the most, so a test ride of all four is in order. 

Let's dissect each bikes strenghts and weaknesses so you know what you're in for. The TVS Ronin is a relaxed, comfortable, peppy and relatively fuel-efficient machine. If you don't mind how it looks, the Ronin is a machine that will keep you satisfied for a long time.

The Yamaha XSR155 is essentially a handsome MT-15 with some small ergonomic changes. It is the sportiest machine of all the bikes you're considering and that reflects in its canted forward riding position and stiff suspension setup. If you have good roads around your residence, then the XSR makes for a compelling purchase.

The Royal Enfield Hunter 350 and the Honda CB350 H'ness are similar machines with somewhat familiar riding experiences. Both are comfortable, look good and have big, torquey air-cooled engines. The difference is that the Honda feels like a more substantial bike that needs a little more effort when riding, owing to its super tall gearing - not necessarily a bad thing, if you're into this sort of thing. 

The Hunter will feel smaller, lighter and more flickable inside the city. Additionally, its well-judged gearing will ensure you don't have to make many gear changes. 

Take a comprehensive test ride of all 4 before you decide.