These are the cheapest line of headphones made by Ultimate Ears and are targeted at commuters. Of all the series, these are probably the least worthwhile to get with the lowest-end lines being roughly equivalent to ear buds. For the same price, you can get much better sound quality, better isolation from cup headphones. In terms of cost and portability, they are probably one of the best out there, but just getting slightly larger headphones in the same price range is a better idea.
The next price step is targeted simply for music lovers. These are good quality pieces that do justify the rather higher cost. They are a touch too expensive for walking-around headphones, though, and not quite good enough for professional use. Actual speakers almost always perform better than headphones, which is another consideration. This series is good for office employees who want good quality sound and a decent amount of sound isolation. This line is a good choice for the cubicle dweller.
The LE TripleFi Series is substantially less money than the LE Custom Series. In comparison, the cost of the TripleFi models are less than half of most of the custom versions, but provide roughly the same quality. The fit will not be as comfortable as a custom monitor, but the sound quality is amazing for the price. More extreme audiophiles and professional live musicians will be able to get the LE Custom quality without the much higher price with this series.
The most expensive line produced by Ultimate Ears, the Custom series is basically the best of the best for in-ear monitors. These monitors are hand-made specifically to fit your own ears. The company actually requires buyers to get an inner ear mold made by a qualified audiologist in order to get this series. This is a fairly quick and painless procedure and ensures the best possible fit. These are expensive, but people willing to spend the money will get in-ear monitors that fit their ears perfectly with great sound quality. Professional musicians desiring discreet monitors will not go wrong with this line.
One thing to bear in mind is that in-ear monitors are limited by the size of the speaker. No matter how well made it is, much more inexpensive speakers and even cup headphones can produce better sound quality. In-ear monitors are a practical tool for musicians, but other designs of speakers and headphones do have some advantages over monitors in terms of quality. In-ear sizing is not a requirement for every music listener, so bear that in mind when deciding on what series to get.