I did not have a budget in mind, and was willing to spend upward to $200 for a nice pair of in-ears. However, I do not believe expensive = good sound, and was willing to try out a bunch of well-reviewed earphones in different price tiers. After reading an extensive number of reviews, I narrowed down my choices to the following: Xiaomi Piston 3, Yamaha EPH-100, and the Dunu DN-1000
Now, the Xiaomi Piston sets (both the Piston 2 and Piston 3) have popped up again and again as recommendations in IEM reviews, but unfortunately I was a bit skeptical because of their price ($20 according to most sites, though I found mine on GearBest for even cheaper - $12). Regardless, the Xiaomi I ordered ended up being the last one to arrive, so I tried the Yamaha and the Dunu first.
The Yamaha EPH-100 I received was a potential counterfeit, since it was an open-box item and has the pronounced grooves on the housing, and I simply don't think they sounded any good - enough to draw suspicion. So I will not include the Yamaha in my comparisons.
The Dunu DN-1000 ($160 brand new from Amazon) on the other hand sounded absolutely fantastic, and right off the bat I knew it was a keeper. The Xiaomi Piston 3 had a VERY tough job measuring up to the Dunu for sure - in fact I was quite sure I would give it a few minutes when it arrives, go "Meh..." and put them aside. No big loss for $12, right?
Boy, was I wrong.
Materials and craftsmanship are all top-notch. The Piston 3 uses a lot of metal - and while the housing has more plastic than the Piston 2, I find the design to be better-looking (and reportedly the Piston 3 is far more comfortable). Plenty of earphones in the sub-$100 category feel more tacky and plasticy than this.
Of the three IEMs I tried, the Piston 3 is actually by far the most comfortable and easiest to fit. To be fair, it has the most shallow fit of the three, but it sits very snug in the ears without putting too much pressure. Superb ergonomics.
The Piston 3 is reportedly much more balanced than the Piston 2. I haven't heard the Piston 2, though the reviews on Headphonelist kind of gave the impression that Piston 3 may be relatively bass-light (just north of neutral). This was not the case at all: The Piston 3 actually has a LOT of bass (more so than I am used to; to be fair my full-sized cans are not bassy sets), and retains pretty good control over it considering the quantity. I would actually rate its bass quantity to be on-par with the Dunu DN-1000, although tightness and extension is not as good.
Mid-range and treble clarity is excellent; these are not muddy-sounding in the least. I simply cannot imagining getting a better sound for this kind of money.
Nit-picks? Sure, there are a few issues. My biggest gripe with the Piston 3 is there's too much lower-treble energy relative to the mids, which causes certain instruments to sound too sharp/metallic and unnatural. Depending on the recording, metallic instruments can sound a tad "splashy" while strings (particularly violins) can sound a bit screechy. I also noticed some unnatural artifacts in certain tracks (soundtrack from Gravity for example) that seems to be the result of peaks in the treble. All in all it's not bad, and only surfaces during certain recordings, but it's something worthy of note.
Mid-range is a recessed, especially evident when cross-comparing with the Dunu. Voices have real weight and presence on the Dunu, whereas they sound more distant and withdrawn on the Piston 3. It's not a dealbreaker for me, but if you like mid-centric headphones you may find Piston 3's V-shaped profile bothersome.
Bass extension on the Piston 3 is good but the emphasis here is definitely on the mid-bass (I tend to prefer headphones with sub-bass emphasis, as they tend to offer a clearer presentation). On tracks that have mostly mid-bass, the perceived bass quantity and quality between the Piston 3 and the Dunu are actually quite similar. But the moment the sub-bass comes in, the Dunu flexes its muscle while the Piston 3 takes a backseat. Bass tightness is more than adequate for this price range, clean with very fast decay. Only on the most challenging tracks does the Piston 3 struggle (Afro Celt Sound System - Big Cat: The Piston 3 clearly runs into trouble at the rapid-fire bass at 5:50, whereas the Dunu DN-1000 and AKG K553 renders this part with no issue).
But like I said, these are nitpicks considering the price. Xiaomi could be selling these for $50 and people would still be talking about them - let alone the $12 I paid for them.
Are they "giant killers"? Well, depends on how you look at it. The Piston 3 are excellent but if you have experienced good headphones, then they certainly won't replace the good sets you have. But for inexperienced people looking to be introduced to high-fidelity sound in their music, I can't think of a better place to start than the Piston 3 (the excellent packaging makes these excellent gifts for friends who are still using their crappy cellphone earphones).
In fact I am ordering another pair of these for a good friend right now.
The fact that I am keeping these after having heard the Dunu (over 10x more expensive) speaks volumes for the Piston 3.