Occasionally having a passing interesting in Vexillology I looked into the meaning behind symbols in the Canton, the top left corner of a flag. The UK has used the Union Jack (technically the Union Flag) in the canton as a symbol of colonial or territorial ownership of places such as the Falklands, St Helena, Ascension, Bermuda, Turks and Caicos, the Cayman Islands, Monserrat and the Pitcairn Islands.
In terms of design I always look at Canada's flag to be one of the world's best, simple, striking and uniquely identifiable as Canadian. Their previous flag had a Union Jack in the canton and was a bit of a mess. No allegations that changing to the maple leaf would dishonour Canada's history. You can add other places like South Africa, Jamaica, Hong Kong, Barbados, Myanmar, Singapore and India that ditched the Union Jack at some point in time and adopted a more aesthetically pleasing and symbolically appropriate flag.
Design wise I admire these
new Australian state flag designs based on a southern cross in the hoist third.
As to add aviation related discussion to this thread as it should have, well I guess airlines can paint whatever they want on the side of their aircraft! There's no reason or requirement they even have to have a national flag there. Air France, British Airways, Air New Zealand, are examples of "flag carriers" which don't have their nation's flag painted as a whole on the side of their aircraft, which is usually to the rear of the fuselage near the registration.