First we need to know whether we need an earphone or headphone, and then we need to know the using invironment, after that we select the right earphone or headphone we need. For example, if we use it for walking, then we need a sport in-ear headphone, and it is mainly for playing music. If we use it for listening to FM, then both earphone and headphone is ok, but it is better to have an audio type headphone, not music type, because audio earphone performs a more clear human voice!
Usually, the warranty for an earphone or headphone is 1 year. Because headphone is a frequently using consumer electronics product, the plastic cable usually can not last a longer using time than one year. However, if we take care of our earbuds or headset, we can use it for several years. Usually, the longer time using, the better sound it performs!
For a wired earphone, the total length is about 1.20M, some maybe a little longer than 1.20M but usually not longer than 1.30M, because if the earphone total length is over 1.30M, it is too long for our daily using, not convenient! For a MP3 headphone, the total length is same as earphone. But for a gaming headphone, the length is from 1.80M to 2.20M, because this headphone is used for desktop computer, so the cable must long enough!
Yes, two speaker earphone has a much better clear sound and stereo! and more spacious balanced frequency response than single driver earphone. Because there is two driver, one driver is mainly for low frequency which is from 10-3000Hz, the other one is a high frequency driver which performs frequency range of 3000-20000Hz very well! The two speaker combined together to have a better sound quality than single driver earphone! We can clearly feel the advantage by comparation between dual driver and single driver earphone.
Different people like different sound quality, for example, some people like deep strong bass, but some people do not; some people may like a clear high frequency or balance sound quality! Even people from different area has a different judgement of the sound qualtiy. However, there is a sound quality that most of the people like, then we can say this is the best sound quality, this sound quality usually has a wide range balanced frequency response, more spacious and better stereo feeling, like we are in the conert. And there is no standard of the best sound quality so far!