Hanoi is awesome.
I did a street food tour which was just amazing - as well as some monuments and museums.
Plenty of things to do and see - the lakes make it a delightful city.
The French quarter and the Old Quarter very worthwhile places to wander around in.
HCMC is just big noisy hot and humid, however the Mekong Delta is awesome.
maybe plan to spend a few days on a river boat - maybe not see anyone but Vietnamese for a few days, really experience the way of life