Mekong Delta Tour from Phnom Phen to HCMC?

While travelling from Cambodia to Vietnam I wanna use a Mekong Delta tour leaving from Phnom Phen and ending in HCMC (former Saigon). Any recommendations about that?
Which are good companies? How much will it cost?
What is recommended 3D/2N, 4D/3N?
Are there places that are not to be missed?
Is it a better option than going to HCMC and take a Mekong Delta tour from there?

Thanks answering,

Harry
(p.s. I know I have to arrange my Vietnam visa before leaving Cambodia)