As said , Hanoi is great, especially the old quarter area which still has architecture from several European countries. This area has wonderful old style accommodation some vey cheap, some a bit more expensive, and great food / big variety, reasonable prices.
I've been to this area many times on days off from giving uni lectures (all English, great students, intelligent, analytical, all speak very advanced English).
Haven't done t it but I've read before that some agencies / hotels / restaurants offer excellent whole day / half day guided walking tour of the old quarter, guides speaks English.
Enjoy.