I was in Vietnam last month for 7 days, spending 3 nights in Hanoi and 3 in Hoi An. While I've been to HCMC and Hanoi several times I hadn't been there recently. I was pleasantly surprised with Hoi An and would have spent more time there and less in Hanoi if I was doing it again. It has the quaint city plus the beach. The pollution and traffic in Hanoi (and HCMC) are oppressive.
Neither have much in the way of gay places, but there are plenty of guys the apps if that's what you're seeking.