Take the direkt bus from Saigon to Phnom Penh, that'll save you money and nerves... and at all costs avoid Delta Tours - this is not a one time mess up, we went to the Cu Chi Tunnels (STA travel outsources to them) and it was only slightly better.
The details: I went through the Delta to Phnom Penh and was prepared for a lot of the usual tourist "attractions" as in visit to a candy making business, tasting of fruit and honey and such. I was not prepared for the organizational chaos: They combined 1, 2 and 3 day tours, so us 3-day people were passed on to the next tour guide and bus every day, which didn't work smoothly at all. The first day, they forgot to count their passengers and I only found out by chance I was supposed to be on a different bus which had already left. My luggage however was on this bus, which luckily drove back for me. The second day, they arrived with a normal SUV to pick up 10 people and luggage, and they had to phone in another minibus which was also relatively full. A lot of the luggare went on the roof (which is fine by me), but they had to borrow strings and expanders from us tourists since they were not prepared (which is not ok). The last day, the boat broke down on the Mekong. Luckily a Khmer fisher towed us to shore, were we waited - now with 14 people - to be squeezed in a normal minibus. I travelled a lot in Asia, but I have not been in a bus this crowed, and while the breakdown of the boat may or may not be bad luck, the bus was definately to save money at our expense.
Also: Each night there were discussions because the guides told people they had not paid for AC and had to do so now (keep at least pictures of your receits!) and the stops at a farm, a Cham village and such consisted of dropping the tourists off and telling them to be back at a certain time. There was no explanation of guidance at all.
If you own or manage Delta Adventure Day Tours, register now for free tools to enhance your listing, attract new reviews, and respond to reviewers.