Of the three bikes you've shortlisted, the Triumph Scrambler 400 X will be the best all-rounder and will also be very easy to ride inside city traffic with its tractable engine and short gearing. 

While the RTX 300 has slightly better suspension travel and composure, it is still a new product, and it would be advisable to wait some months before buying an all-new machine like this, so if there are any teething issues, they can be ironed out. 

If you are open to having a retro riding experience, then the Royal Enfield Bullet / Classic 350 are worth looking at. These are very comfortable machines, although their performance won't be anywhere close to as sprightly as the other bikes you're looking at. 

On the plus side, the Bullet/Classic are much more affordable to purchase. 

We'd recommend a test ride of the RE 350s before you make a decision. 

Since you've said that this bike will be used mainly for touring and occasionally in the city, the Royal Enfield Himalayan 450 makes more sense over the Triumph Scrambler 400 X. That's because the Scrambler's shorter gearing will result in the engine feeling like its running out of breath past 100kph and also because the Himalayan is a more spacious machine that was purpose-built to cover long distances. 

Royal Enfield's service experience varies from city to city and, in fact, even person to person. So we would advise you to pay a visit to your nearest authorised dealer and service centre to get a clearer picture.

You should also take a look at the KTM 390 Adventure X because it has good road manners and will be the quickest bike of these three. It also comes standard with cruise control, which will be a boon for you on long days in the saddle. 

In fact, if you don't want tall motorcycles, the KTM 390 Duke will make for a good touring partner, and you'll have way more fun on twisty roads, although you will sacrifice some comfort compared to the ADVs.

A test ride should help you make a decision. 

A radiator guard is a good idea for any liquid-cooled motorcycle - like your Triumph Scrambler 400X - especially if you plan to ride off-road. It will protect the radiator from stones and debris that can be kicked up by the front wheel, which can damage it and cause you an avoidable expense. 

If you get your bike pressure-washed often, a strong stream of water can also bend or damage the fins of the radiator. So, the guard will also help you in this situation. 

A well-designed radiator guard from reputed brands or the company's accessory catalogue itself will not affect the bike's cooling in any way. It is designed to allow air to flow through it to cool down the hot coolant, so the radiator can do its job efficiently. 

Of the three bikes you're deciding between, the Triumph Scrambler 400 X will be the most capable machine in terms of carrying a pillion and covering distances. This is because it is the largest feeling bike here with the best suspension comfort and spacious seats. Its 40hp engine will also give you levels of performance the other two air-cooled 350s won't be able to match. 

However, if you are a relaxed rider, then the Honda CB350 and Royal Enfield Bullet 350 will be right up your alley. Both have smooth, torquey air-cooled engines, wide and spacious seats, and good suspension.

It all comes down to what sort of riding experience you prefer. We would recommend a test ride of each bike with your preferred pillion so you can make a more informed decision. 

Taking your considerations into account, bikes we would recommend taking a look at are the Triumph Speed 400 and Scrambler 400 X / XC. 

Both will offer you considerably higher performance than your Yezdi bike and will also be comfortable enough to handle daily commuting duties while being brisk enough on the highway as well. 

If you want an air-cooled, torquey engine, then you could even take a look at the Harley-Davidson X440, which is a comfortable neo-retro roadster that has decent performance. 

Take a test ride of the machines you shortlist before picking one. 

Between the Honda H'ness CB350 and the Triumph Scrambler 400 X, we would steer you toward the Triumph bike purely because it offers you significantly higher performance for not that much more money. The Scrambler is also a smooth, comfortable do-it-all motorcycle which has good passenger accommodations as well. The H'ness is also comfortable for two-up riding and is a good city bike, but it will not be able to match the Triumph's performance advantage. 

We would advise you not to go for the Royal Enfield Super Meteor 650 because it is a rather heavy bike at 240kg, which will not be the best fit on traffic-riddled city roads. Moreover, its stiff rear suspension will be the bigger reason to look elsewhere. If you want a RE 650, we would recommend taking a look at the Royal Enfield Interceptor, as that has more pliant suspension and is also much lighter. 

Since you have mentioned you want a powerful motorcycle, we would recommend you look at the Triumph Scrambler 400X, KTM 250 Adventure and TVS Apache RTX 300 in the ADV / Scrambler category. Of the three, the Triumph bike is the most powerful, but it is also pleasantly usable inside the city, whereas the KTM and TVS are more do-it-all machines that will also be wonderful on a day-to-day basis. 

Coming to the Xpulse 421, there's no official communication from Hero on when it will be launched, so we would recommend going with any of the other options you are considering. 

Take a test ride of whichever option you shortlist before you choose. 

Both the Bajaj Dominar 400 and Triumph Scrambler 400 X are reasonably reliable and hassle-free machines, and considering they are both made by Bajaj, they should be light on the wallet in terms of maintenance. We recommend choosing the one you are more comfortable with and the one that has a service centre close to you. 

Coming to why we haven't reviewed the 2025 Dominar 400, that's because the bike is mechanically the same as when we reviewed it last in 2021, and the only tangible difference is the new LCD borrowed from the Pulsar NS400Z.