We did this trip with Vietnam Airlines and they were fantastic.
I highly recommend Vietnam airlines
You're stuck with Vietnam Airlines (Angkor Cambodian Air) as they are (as far as I'm aware) the only airline that flies the route. Pricey too!
I would suggest going by route as it is much cheaper.It takes around 6 hours from SaiGon to PP and this place is worthed to spend a night at least before headhing to Siemreap.
But if you have no problem with paying and tight on time then you have to Stick with Vietnam airline coz no other choices.
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