I have flown VN
, Air Asia, and Siem Reap Airways (and MH
but that was a long time ago).
SIem Reap Airways is basically the Cambodian version of Bangkok Airways. They managed to serve a snack and drink on the short hops from Siem Reap to Phnom Penh. Overall, their service is excellent, both in the air and on the ground. The plane I flew was an ATR-72 which only had Y class seating w/o any IFE.
I flew VN
only once, within Vietnam. They also provided a drink and snack service on the 1 hour long flight from Danang to Hanoi which was on a rather modern Airbus (A320?). The flights were on time and my overall impression was positive. Seating was ok and no IFE was available butagain these were rather shirt domestic flights. The only problem was booking the flights in Vietnam. I had to go to a local travel agent to get the tickets as internet booking on their web site was not available back then (May of this year).
Air Asia is a low cost carrier. Booking flights on their web site is pretty easy and they have an extensive network of flights in Thailand, Malaysia, and Indonesia. Their service is no frills - you can get express boarding for an extra fee but there are no seat assignments and you have to pay for all food and drinks. They also discourage outside food consumption on the planes. The food offerings consist of various snacks and sandwiches; alcohol is not available on their flights. The seating is also somewhat tight but that is to be expected on a low-cost carrier. Air Asia may still have some old B737-300 aircraft in their fleet which show their age inside. However, these planes are gradually replaced with modern A320 aircraft which are in much better shape. Overall, considering their cheap tickets they are ok if you book them in advance and for flights of less than 2 hours. I am not sure if I would like to fly them extensively on longer flights, mostly because of their cramped seating and total lack of IFE.
Also, Air Asia has a rather limited baggage allowance (15 kilo for checked bags AFAIK) and they sometimes cancel flights or change flight times. That happened to me several times so if you book well in advance you should periodically check your flights. If you are connecting to another flight or simply have to be somewhere at a certain time I would allow for a lot of extra time or have a backup-plan when flying Air Asia.
Have a great trip.