Beautiful Hanoi by night: The Popular Hoan Kiem Lake
The difference between Hanoi and Ho Chi Minh City is the artchitecture. There are more old houses, old buildings and so many lakes that make Hanoi such a nice city including heaps of old traditional workshops. The lifestyle and the people are so different. In Ho Chi Minh City, there still remain lots of nice old buildings. There's quite a few tree lined streets and parks and the people are hospitable and make you feel like you are at home.
The best time to visit Hanoi for those who prefer cooler weather should be between Oct to Feb of the year.
Cheers