Since you have mentioned you want a retro bike and are looking in the 350cc category, you could take a look at the Royal Enfield Bullet 350. It has the same engine as your brother’s Hunter. It will offer you a more spacious riding position and a laid-back riding experience, not to mention more road presence, if that is something that matters to you.
Writing the Yamaha XSR155 off because its engine is “just 155cc” would be a mistake in our opinion. Because its performance belies its displacement, and it will give you great fuel efficiency and also last you a long time.
Take a test ride of these two to see which one suits you better.