aeroline is quite established and they were the first operator to break the monopoly held by "nice coach" on the luxury bus sector between KUL and SIN. However, none of the coaches has personal video and their coaches are slightly older than "airebus". And when I say "slightly older" I dont mean they are old junks like NYC Chinatown buses; average age of "aeroline" coaches are about 3 years compared to "airebus" which is less than 1 year.
While I wouldnt hesitate to travel on "aeroline" (and I have used them in the past), the most comfortable service are the 2 which I have listed above.