Hello Jeni,
I used both system. The first time I went to
Cambodia, I got my visa straight at the Siem Reap airport, I only had to wait like 20 minutes for the entire process. The second time, i use the online form and skipped the visa line queue and went straight to the custom desk. The funny part is that I had to wait outside the airport in the
hotel van for the other guest going at the same
hotel who didn't have their online visa. go figure.