Traveling around these three countries can take a lot of time, so it's recommended to fly between them. Multiple airlines operate in the region, such as AirAsia, Indigo, and Vietjet Air, offering flights to a range of destinations. The costs of flights vary, depending on the airline, time of travel, and how far in advance tickets are purchased. A flight from Bangkok to Siem Reap will take around 1 hour and cost around $50-100, while a flight from Siem Reap to Ho Chi Minh City will take approximately 2 hours and cost between $80-150. Be aware of your transit time when considering travel costs and ensure to plan accordingly to avoid delays.
If you have more time, it's highly recommended to spend more time in each city to fully experience the culture, food, and attractions they offer. Adding one or two nights at each location is ideal to provide ample time for exploring, plus it allows extra time to visit places you might miss otherwise. Additionally, consider booking tours in advance to ensure success and save time. In contrast, if you have less time, consider skipping certain attractions that are less interesting to you or scaling back some time in transit. However, ensure to prioritize your preferred destinations and allow enough time to take in the surrounding scenery without feeling rushed, and anticipate your travel time, plus some extra time to have enough time to navigate and experience the local culture.