Etymotic ER-4S MicroPro Reference

Pros: Extremely clear, uncolored, detailed sound; sparkling treble, deep, tight bass, smooth mids

Cons: Cable noise

Summary: This is flat-out the best universal fit in-ear monitor money can buy. Some people have claimed that the sound is harsh, or tipped toward the treble region, but this is completely, utterly, false. They are by far the smoothest, most neutral, most accurate, most detailed, most musical IEM I have ever used. I would even say that they are lush. I have never been able to enjoy music quite like I have with these. The frequency response was always off somehow. Too much bass, or not enough treble, or dim, distant mids. But these, wow. They let me forget that I am wearing headphones and allow me to truly delve into the depths of whatever I am listening to. The sound they produce is so smooth and natural I don't even have the vocabulary to describe it. For the mids, think smooth, like freshly churned butter, and just as delicious. For the highs, think clear and sharp, like a polished diamond. For the bass, think deep like the mariana trench. The sheer naturalness of the sound is something to behold, and the detail, the ability to discriminate between sounds, the ability to hear each instrument exactly the way it sounds, the ability to hear even the smallest background noises, is unsurpassed by anything else in this price range.

Truly a king among headphones. I'm ashamed I didn't buy them sooner.

Phew. Now, for the cons. The cables are very noisy. Noiser than any other IEM cables. You must use the shirt clip or find some other way to secure them or else the transmitted noise will be very disturbing. Potentially, they may be uncomfortable for some people, but I have yet to have any problems. With the foamies or Comply tips, I can wear them for hours on end with no discomfort. Undoubtedly, some people will find them uncomfortable.