Hello my readers!
As I have found it a little challenging to find information about reliable bus connections in this area, so I want to share what I have done.
This whole area is covered by company called Mekong express which was also recommended to me, but as I travel on tight budget, I was looking for cheeper options.
I have found a nice bus from Ho Chi Minh for half price! :-)
Company called Kumho Samco Buslines connects Ho Chi Minh and Phnom Penh and runs daily buses at 7am, 8am, 9:30am, 11am, 13pm, 15pm. Here is their card with all other details. In Phnom Penh, they can drop you off if your address is on the way to their office, otherwise you get off at the office. It is not far from center at all. If you feel like tuk-tuk, never pay more than 5$ (more likely just 3$) and for motorbike taxi just 1$ is a good price, unless you cross the whole town.
Later on I was looking for a direct connection from Phnom Penh to Bangkok and again, I found many complicated ways how to do do this journey, but nothing direct. But I asure you, it's easy and OK, if you don't mind 13 hours on a bus. I know it's a lot, but do you want to pay the high fee for leaving Cambodia by air?So Capitol is the answer: http://www.capitoltourscambodia.com/contact_us.php
Nice and reliable company, can book you a seat over a phone as well. Bus leaves once a day at 6:30 am from the company office. It costs 18 USD, so don't pay at agents, go strait to street 182 and buy the ticket there. We took the southern road (not through Siem Reap). The road is OK there and it took 8 hours to the border (as bus delivers things and drops people off). At the boarder, wait for another employee of the company to come aboard, he speaks English, gives you another ticket for the driver on Thai side and shows you the way to immigration. ;-) Yes, easy right?
Now once you are on Thai side, hold your new ticket visibly and people will point you out to he right minivan (in front of 7eleven) once all customers cross and sit, bus is ready to go. It takes another 4 hours to Bangkok (with one stop). Drop of is at Khaosan road or Victory monument (sky train). Or just speak to the driver at the break time, when our driver was visibly more relaxed and talkative.
Wish you a safe journey!!!