Hi, I’m 47 years old, 6 ft tall, and my son is 21 years old, 6’3″ tall. I’m looking to buy a Royal Enfield Classic 350, but my son is interested in the Classic 650. My main concern is mileage, as we’ll do more than 95% city driving. Could you please suggest which bike suits us better?

Since almost all of your usage is going to be in the city, going for the Royal Enfield Classic 650 doesn't make sense because its rear suspension is quite stiff, and in traffic, its 243kg kerb weight will be a task to deal with, especially considering the way the engine will splay your legs out. You are right to worry about fuel efficiency because the 648cc twin is not very fuel efficient at slow city speeds, especially considering the bike's 243kg kerb weight. 

The Classic 350 is a lovely bike to use inside the city with its upright ergonomics, plush suspension and torquey, soulful engine. The Goan Classic is also something you can take a look at if you like its custom bike look, although it does trade off a little bit of practicality and comfort to the Classic.