When it comes to cappuccino and flat whites the flat whites are stronger than cappuccinos.
A flat white is lower in calories than cappuccino because of the less milk content.
The cappuccino has a better taste to it than flat white because of the added milk, sugar etc.
If you're on a diet then you would want to drink the flat white instead of a cappuccino because the flat white is lower in calories.
But you can drink some cappuccino in moderation and still lose weight as well but don't overdo it.
Too many flat whites or cappuccinos can be bad for you health when you drink it in excess but in moderation it's healthy and okay.