Booked trip to Vietnam for 13 nights from Feb 24. We fly into Ho Chi Minh have only booked 3 nights accommodations and 3 Nights in Hanoi.( we are flying out of Hanoi). We booked an overnight cruise in Ha Long Bay.
We plan to visit Hoi An, Da Nang and Hue but haven’t book accommodations yet. With 6 nights left should we visit any other cities?
Any suggestions? How many nights should we book for Hoi An,Da Nang and Hue?

I’d say 2-3 nights in Hoi An would be good; consider staying a couple nights in An Bang beach before or after. Amazing beach, really laid back place. When we were at An Bang note there were no bank machines in town. Stayed at La Siesta in Hoi An and were not disappointed, great place (note though it seems the name has changed to that since we’ve been so not sure if same owners). Find the Banh Mi queen while you’re in Hoi An.

Our favorite place is Hoi An, 45 minutes South of Da Nang. We stay at the Sun Boat Hotel. Make sure you ride the pedal bikes through the rice fields.

In Hoi An I stayed at The Jade Hotel. Inexpensive and included breakfast, had a nice pool and lovely staff. Can walk or cycle to the Old Town. Can cycle or scooter or taxi to An Bang Beach.

Did day trips to My Son ruins and a cooking class. The transport to cooking school was in a round basket boat. It was so much fun!

I'd highly recommend Hoi An and Hue.

Your itinerary sounds great. I wouldn’t worry too much about Da Nang, it’s a modern city and thus (to me, anyway) less interesting than places like Hoi An and Hue.

We did hanoi, hue, da nang, ho chi minh, etc. and tbh if I did it again, I would skip ho chi minh.

I was just in Vietnam in November and many of the people I met spoke highly of Da Lat. I didn't get a chance to go, but it sounds like a nice place. Our Cu Chi tunnels guide said it was very peaceful and romantic.

This are the places and timeframe I would recommend in Vietnam. Hagiang loop 9 days
3 days Hanoi
3 days Catba Island
2 days Sapa
2 days Ninh Binh
3 days Phong Nha Kebang
2 days Hue
3 days Hoi An
2 days Dalat
2 days Muine
3 days Ho chi Minh

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Most people prefer HoiAn, we liked them all. Hue has no beach and less restaurants, it just felt less smooth as a tourist destination, but with lots too see, maybe it’s more Vietnamese? We did great bike and scooter riding around. DaNang is a booming modern city with a great beach. We loved the Hoi An Sincerity Hotel, we got free bikes and or shuttle to the beach and town. If you can drive from Hue to DaNang and stop along the way it’s great. Halong Bay is now very dirty and over crowded.

Following.

We really liked Dalat, I’ve alway wanted to go back. there’s also North oh Hanoi, Sapa is soon going to be completely overrun, but if you stay outside? We did a trip to Ban Gioc waterfall (google it)I would recommend taking a few days for that.

Two to three nights in Hoi An, so probably nice pace for the time you have.

Hoi An deserves at least two days..not to be missed.

I’m doing a similar trip at the beginning of March but I’m the opposite direction. That seems to be the places to stop, but I’ve recently discovered Dalat. I’m thinking I’ll take a detour through there for a night or 2. Check it out

It is a lovely city. It is considered the Honeymoon Capital of Vietnam. Great day tours from there as well as a gondola ride.

Thank you everyone for all the suggestions.