Northern Vietnam :
It stays "soviet". Roads and transportation are not really developed, travelling without an agency is hard, few companys, few cars... Hanoi is still the famous old city : no new building downtown. Maybe that's the reason why Hanoi keeps so much charm ?

Cat Ba Island :
The Island is developing its touristic building but is still calm.
Agencies often offer a forest hiking passing 6 mountains. In fact the way stays under trees, you can't see any sceneries. Nothing amazing. Moreover, in case of rain, the last downhill is really slippy, on cutting rocks. It can be dangerous. You can prefer to spent the whole day on a white sand beach.

Southern Vietnam :
Southern Vietnam has fallen in capitalism. Ho Chi Minh always seems to be growing. Private transportation companies and good roads exit. It's easier to travel by yourself.

Phu Cuoc Island :
Facing the Cambodia coast, the island is still not too crowded.
There are some hotels close to the beach. People wish you nice day without trying to make business.
Local speciality : tasty black pepper.