The logistics of first time in Southeast Asia

It was very hot when we were in Cambodia, Vietnam and Bangkok in October. Locals said January is better. We used cheap flights, new planes, on time with Air Asia and Vietnam Air. You can also travel on the Mekong River.

The weather was just fine for us last late September to early October in Nepal, Thailand and Cambodia. Easy regional flight connections. Haven’t been to Vietnam but literally all friends visiting there rave about it. Do a bit of research and then just do it!

We just returned from a 2.5 week to,ur of Vietnam, with 2.5 days in Siem Reap. HCMC and SR were extremely hot, 90 or so, with high humidity. We had rain in Hanoi and Danang. Our guide told us that it was supposed to be the dry season, but the weather is changing (sound familiar?).
If you look at a map,you will see that Vietnam is very long, with the cities spread out along the coast. That is why tourists often fly from one to another.
I would have loved to have at least one more day in Cambodia.

Best time to go is during our winter when it won't be as hot and humid. Avoid the summer months (May - Aug).

With 3 weeks, you can do any of your options. I would look to fly most of the segments unless you are trying to experience the train systems. There are lots of low cost carriers and if booking in advance, you should be able to get cheap flights.

If you are up for flying, I would recommend doing a sampling of places and combine Thailand, Cambodia, and Vietnam but this is what I would go for.

I would do something like this, allowing logistics to be taken care of by a tour leader.
https://www.gadventures.com.au/trips/essential-vietnam-and-cambodia/4643/
Some time in Singapore beforehand then fly to Hanoi for the tour. January is regarded as the best time in Vietnam.

Definitely November-February time frame if you want the least hot weather. It will be hot and muggy no matter when you go. I went in late March and it was borderline uncomfortable. It's different hot/muggy than you're used to in Maryland (and for an Oregonian like myself, it was positively soupy, and murder on curly hair!). The only difference is the highlands near Hanoi can get cooler, but not arctic temps. No matter when you go, plan ahead to make sure you get your Vietnam visa in plenty of time, and triple check the dates on it before you leave, they're not keen on improperly dated visas.

I took a Gate 1 tour of Bangkok, Siem Reap, and five cities in Vietnam (HMC, Hoi An, Hue, Halong, and Hanoi). My trip had four flights - the public transport is not easy and SUPER slow, so it is true flying is a more efficient way to get around. Since you're planning three weeks you can spread out the flying. I found the Lonely Planet guide books and Trip Advisor forums helpful for planning purposes.

Personally, I would definitely fit in a trip to Siem Reap for Angkor Wat (bucket list worthy) because it's such a long flight over, you might as well go. Cambodia does visa on arrival, easy. And though each of the cities in Vietnam I went to had positives, my most favorite was Hoi An (so pretty and rural - I can recommend a great cooking class if you go there). HCM is a big, very busy, city - interesting sites, but I would not have enjoyed a long time there. I would pick Hanoi as my "big city" experience. PM me if you have questions.

Thanks for all of your replies. After doing a lot more research, this is the itinerary I'm working with so far (starting 1st week of November):

Hanoi - 3 n
Ha long Bay - 2n
Hoi An - 4 n
HCMC - 3 n
Phnom Penh - 2 n
Siem Reap - 3 n
Bangkok - 3 n

Im considering shortening it by a few days, my first cut would be dropping PP entirely. Also, may go down to 1 night I Ha Long Bay. Any thoughts on this?

I lived in Cambodia for 7 Years and have been to almost all of SE Asia many many times over 35+ years. So I can offer some insight.

First of all Thailand is the easiest country to travel in in an area where travel is very easy overall. Thailand is a fully developed industrialized country on the verge of 1st world status. Holding it back are it's Monarchy and turnstile governments. Vietnam is incredibly diverse and a pretty big country. The food, especially the seafood is exceptional.

Having said that I think the two most interesting countries in the area are Laos and Burma (Myanmar). Luang Prabang in Laos is a true jewel and should be visited if possible.

Travel in the region is very easy. All major cities are covered by multiple flights which can be very cheap. A regular overnight train runs from Bangkok to Vientiane where you can get a bus to Luang Prabang.

While I would recommend a visit to Siem Reap and Angkor (there are many ways to get there including bus and mini bus and air from BKK) I would not spend too much of my first visit in Cambodia. And to tell the truth while I love the Cambodians it is the most dangerous country of all the rest. Thailand, Myanmar, Vietnam, Laos and all the rest are very safe for tourists.

Keep in mind the flights in the region are short and cheap and a lot more comfortable than a minibus trip. The large Buses can be a very good experience or a bit on the Disneyland "E" ticket ride variety.

I would do 3 weeks if I were you. and do the "Taste of SE Asia" approach. One week each in Thailand, Laos and Vietnam concentrating on the high points. (By the way do not miss Hanoi, it's truly one of Asia's most lovely and enchanting cities.

Best time to go: Yes most above are correct Dec Jan Feb are the most reliable time for all of them. November can be very good also. March April and May are HOT and WET The rainy season is beginning. (During my time in Cambodia one year it rained CONTINUOUSLY 24 hours a day for 20 DAYS) Now the biggest outlier for the weather will be Vietnam. It's monsoon is a bit different from the rest of Mainland SE Asia. But the winter months are still the best.

I can give you tons of recommendations but it would make this too long and may not fit your interests feel free to message me if you want. I'd be happy to help.