There are many different areas where one can find good Wifi hotspots in Vietnam such as:
Coffee shops: There is free Wifi at most coffee shops in Hoi An, Ho Chi Minh City, Hanoi and Danang. Certain suggestions are Highlands Coffee Shop, Trung Nguyen Coffee Shop, Angel in US and Gloria Jeans.
Fast food franchises: There are many fast food outlets in Hanoi and Ho Chi Minh city such as Jolibee, KFC, Lotteria and Pizza Hut that have good Wifi connection.
Hotels and office buildings: Most hotels will offer tourist Wifi at discount rates and the connections are pretty good.