I'm a Grado lover. During a recent road trip, I came to realize the virtues of sound isolation. That's when I went through thread after thread looking for the right IEM. Not completely sold on any one design, I ordered the five that inspired the biggest buzz:
Etymotic Er4p
Shure SE530HTP
Westone 3
Westone UM3X
UE Triple Fi 10 Pro
Of these, my favorite is the Westone UM3X. I like it because it's ergonomic (fits into my ear like a hearing aid), looks cool (transparent) and - best of all - has a killer sound without killing my ears. There's a running debate about whether the Westone 3 has better bass. In my opinion, the W3's bass is highly pronounced but it's more of a midbass. The UM3X has a more neutral sound. Some find it clinical. I find it terrific. I prefer its presentation to W3 as well as to all of its rivals.
That said, I think the key to getting great sound is finding the right tip. Everybody's ear is different. I can't even use the same tips on different IEMs because their architectures vary. For the Westones, which curl up in my lobes like a hearing aid, the fatter tips work better because that's the wider part of the ear canal (at least for me). The SE530 works much the same way. I don't find it as ergonomic (It slips out more easily) but it also provides great bass with big foam tips (at least in my ears). If I use the Er4p or the Triple Fi 10, I have to go with smaller tips, because they sound better deeper in the ear canal.
My favorite bass - once the right tips are used - comes from the UM3X, the Triple Fi 10 and the SE530. The W3's bass is bassier than I need and more midbass than anything. The Er4p/Er4s must have a higher impedence because the output is at least several decibels below that of rival IEMs. The Er4p is made to run right off an iPod, which it does, but you still need to adjust for that several-decibel drop. Those who complain that the Er4p has no bass are likely failing to adjust for the difference in output. When I finally got the tip right, and I adjusted for the output, I got plenty of bass - and that was before I"d hooked up my M^3.
If I had to give a nod to one of these, it would be the UM3X - not exclusively for the bass but for the overall presentation. For my money, it has as good a bass response as any of the others and it sounds phenomenal. But that's if I had to pick just one. I very much like the Triple Fi 10 and the SE530. Right now, I"m not in love with the ergonomics of the Er4p but the sound is great once you get the right fit.