Looking the best way from Ho Chi Minh to Siem Reap? Vietnam and Cambodia are pretty close and the two countries share 3 international border crossings.
There are many tourists in Cambodia from Vietnam and vice versa. And among all the cities of Cambodia, Phnom Penh and Siem Reap are the two cites that people from Vietnam tend to visit most.
Phnom Penh is the capital and the largest city in Cambodia. It is also a famous destination to the tourists for many traveling attractions. While Siem Reap is another famous tourist city of Cambodia with also a lot of well-known travel sites.
Although the distant between the two countries is close, the transportation is somehow complicated and time-consuming. There are different ways either overland or by plane to travel between Vietnam and Cambodia, not only by plane like the most of other countries. Unfortunately, there is no train to travel between Ho Chi Minh and Cambodia.
And obviously, you need a tourist visa to travel between the two countries. Somehow you can get it at the airport when travelling by plane but you’d better to prepare it in advance.
Following are the detailed information about the transportation from Ho Chi Minh to Siem Reap:

There are direct ways to travel from Ho Chi Minh to Siem Reap. However; because Phnom Penh seems to be the first big stop when you travel from Ho Chi Minh to Siem Reap, most journeys between the two cities drop by Phnom Penh to rest or facilities using before come to the destination.
The following are some ways to get from Ho Chi Minh to Siem Reap:

From Ho Chi Minh to Siem Reap by Plane:

This is the most expensive but the most straightforward and fastest way to travel directly from Ho Chi Minh to Siem Reap.
However; you can save your money by looking for the cheap flights. To get a cheap flight, you can go and search multiple sites online, collect the airlines’ data and choose the suitable one. The ticket price can be adjusted based on the time you book your flight, so decide to book smartly and you can save some money to travel. People say that Tuesdays, Wednesdays, and Saturdays are best days to book your flight tickets and the flights those days are always cheaper than the other.
The flights will take off at Tan Son Nhat International Airport (Ho Chi Minh) and land at Angkor International Airport (Siem Reap) in about 1.5 hour.
From Angkor International Airport, you should take a taxi to get to Siem Reap center which is about 7km away from the airport.
Airlines providing daily flights from Ho Chi Minh to Siem Reap are Vietnam Airlines, Cambodia Angkor Air, the ticket prices are approximately same, under/above $100 for each one-way ticket.

From Ho Chi Minh to Siem Reap by Bus:

This is a cheaper way. A ticket price is just more than $20. But its drawback is that there are breaks along the journey and you have to stop several times which is somehow time-consuming. One of the must-have break is the break for bus changing in Phnom Penh. Almost buses from Ho Chi Minh to Siem Reap have to stop at Phnom Penh to change the bus.
One thing you have to notice that you shouldn’t take the overnight bus just because you think that it is time-saving. The border is closed at night so that overnight bus will likely be time-consuming rather than time-saving. Early-morning bus is a much greater idea. With about 2 hours for bus changing in Phnom Penh, the early-morning buses may get to Siem Reap at 23h in the day, the others may arrive late at night.
There are a lot of bus companies providing journey from Ho Chi Minh to Siem Reap: Sorya Transport, Giant Ibis Transport, The Sinh Tourist,
Sorya Transport:
Add: 301 Pham Ngu Lao st.
Tel: (090) 275 5765
Web: ppsortatransport.com.kh
Sorya Transport provides two kinds of bus journey from Ho Chi Minh to Siem Reap, one is direct and one is via Phnom Penh.
The only bus travelling directly from Ho Chi Minh to Siem Reap departs daily at 6:45 and travel in 13,5 hours. It arrives at Siem Reap at 20:00 the same day. Its ticket price is about $25 per way
The other buses via Phnom Penh are divided into two kinds, departing in the morning and departing in the afternoon.
The only one bus in the morning will depart at 8:00, stop at Phnom Penh for 2 hours to change bus. Then visitors will take a night bus from Phnom Penh and arrive at Siem Reap at 23:00 that day. The price ticket is about $20 for the whole journey.
The other buses in the afternoon depart at 11:30 and 13:45. They take about 1 or 2 hours to rest and bus change in Phnom Penh. Then another overnight bus will continue to get to Siem Reap at 6:00. The ticket price is about $22.
The Sinh Tourists:
Add: 246-248 De Than st.
Tel: 028 3838 9597
Web: thesinhtourist.vn
The Sinh Tourist provides sitting buses departing at 7:00 daily.
Giant Ibis Transport:
Add: 237 Pham Ngu Lao st.
Tel: (12) 0890 2333
Website: giantibis.com
Giant Ibis Transport doesn’t provide direct bus journeys from Ho Chi Minh to Siem Reap. Tourists will take sitting buses from Ho Chi Minh departing at 8:30 and 12:30 to Phnom Penh then take sleeping buses from Phnom Penh departing at 22:30 or 23:00 to Siem Reap.

From Ho Chi Minh to Siem Reap by Boat

This is not a common way to travel from Ho Chi Minh to Siem Reap, because it is not the most convenient of the cheapest way, but if you want an interesting journey with fantastic view combine with visiting Mekong delta, you can choose this one. A part of the journey will be done by boat and the others are buses. In detailed, you have to take a bus from Ho Chi Minh to Chau Doc, then take a boat from Chau Doc (Vietnam ) to Sisowath Quay (Phnom Penh), continue taking another boat from Sisowath Quay to Chong Kneas, and finally take a tuktuk – a motorcycle-pulled carriage to Siem Reap.
Hang Chau is a popular company offering speedboat from Chau Doc to Sisowath Quay. They daily boat departs at 7:30 am and arrives at Sisowath Quay after 3.5 hours. Each price for one person costs $33. (VAT included).
From Phnom Penh, you can take another speedboat of Mekong Explore company to continue your trip to Siem Reap. They provide daily speedboat from Phnom Penh at 7:30 am and the boat will arrive at Siem Reap after 6 hours. The ticket price is from $28.
Traveling by the cruise along the Mekong River from Ho Chi Minh City to Siem Reap is definitely a luxury and heavenly idea. With the high price, you will get the truly heaven-like experience along the river with the picturesque view outside and high-class service inside the cruise. Heritage Line offers an 8 days – 7 nights tour between Ho Chi Minh City and Siem Reap called The Lost Civilization, following is its program in general:
Day 1: Sai Gon – My Tho – Cai Be
Day 2: Cai Be – Sa Dec – Tan Chau
Day 3: Tan Chau – Boarding Crossing – Phnom Penh
Day 4: Phnom Penh
Day 5: Phnom Penh – Kampong Cham (Mekong)
Day 6: Kampong Cham (Mekong) – Kampong Chhnang (Tonle)
Day 7: Kampong Chhnang – Tonle Lake
Day 8: Siem Reap
The program orders can be changed due to the water seasons (low water or high water) and the price is from $1,000 per passenger sharing room and also depends on the levels and the seasons. . You can You can contact sales@asiajourneytravel.com for help and to be provided suitable program.