Great question and to this we say...
Use What you Know
Which audio format is the best? As you will come to find out through study and experience, it really depends on the situation. The finest form is in many cases all about the best fit for the function. So this article is set to explore which audio formats are the "best in class". Industrial perspective can also play a factor in an engineers bias toward one type or another, as rarely used file type likely has little value to that individual. To determine which is, in fact, the best for any given purpose we should seek ask, "what is the intention or use for this file?"
.WAV & .MP3
For many people, the best format is the one that they have immediate need for or interaction with on a regular basis. Given how many people have been primarily PC users and music fans it is no wonder that many people are familiar with the .WAV and .MP3 formats. The prevalence and convenience of these two file formats makes them if not the "best" than the most popular by how prolific they have become.
While it may not be the most efficient option available in today's computing terms, for a long time the .WAV was a way to convert analog music to a high quality digital copy that would play on many devices such as CD players and other computers. Audiophiles in the early days of keeping a digital music library had many of these and this format is commonly available in recording programs today such as ProTools.
The MP3 rose to prominence on the back of portable music players like the iPod. The convenience of its size allowed for vast digital libraries to be carried around in our pocket while commuting or clipped to our clothes while exercising. In the years since Napster, other file sharing networks have risen to make trading massive banks of music all over the globe. This has allowed many fan bases to grow around artists that otherwise would have difficulty reaches the far reaches of the planet with their officially published music.
Somewhere between the cross section of convenience and quality, efficiency and "good enough" is where the trends of people audio file usage resides. Hopefully, this article has helped to inform you about the popular or "best" audio file formats that have been in common usage.