Our airliner sounds are from a 767. I honestly doubt you can find more realistic unless you go for a high quality 3rd party addon for desktop simulator.
Keep in mind that recorded sounds can be VERY different from 1 microphone to another meaning that using random videos you find on youtube to hear what an engine sounds like is not accurate.
We spent a lot of time (and money) on our airliner sound package and we believe we are very close to the real thing for the 767.
Having a different sound package for each commercial aircraft is something we would like to have ultimately, it just requires a lot more time and a lot more money (and access to clean recordings, which is extremely difficult for airliners).
Our 172 is also extremely accurate since we did that one ourselves with the help of a professional sound designer (who also did the mixing for the 767).
Other aircraft (turboprop, fighters) are more subjective but "good enough" (and definitely better than most default aircraft in most simulator I tried).