Avoid the Giant Ibis Bus's when you are in Cambodia. I've been riding them for a few years since they started up, but no more. My last trip between Phnom Penh and Sihanoukville was almost my last trip anywhere. The driver drove erratically throwing passengers around the bus, drove too fast, passed trucks/cars when there were oncoming trucks/cars and seemed wired/stoned. On arriving in Sihanoukviile he also took a dangerous, steep shortcut. At the hallway rest stop I had asked him to drive slower and but he would not listen and drove even faster and more erratic.
I complained to the company and got the runaround. I asked that they fire him before he killed people, but they refused. I asked that they do a drug test of this bad/stoned driver and the company refused. This driver will eventually cause a bad accident and injure/kill passengers. Do youreslf a favor and stay away from this company. There are many new companies running VIP vans on this route and others in Cambodia.
Also, the Ibis bus's that I have taken in the last year, 50% of them the WiFi didn't work and the bus's seemed very dirty. This probably shows that the company puts profit ahead of maintenance of their bus's even though in the past few months they raised there fare by $1.00us.