There are 2 types of drivers for earbuds.
Your cheaper dynamic drivers, and then the more expensive ones using balanced dynamic drivers.
Yes, you can find amazing dynamic drivers on IEMs, but for the most part, the balanced armature ones are the ones you want.
Then there are 2 different types of seating.
Buds (Like dollar store stuff, sony stuff, jelly beans and apple)
And behind the 2nd bend.
Behind the 2nd bend is where you will find all the nicer ones (Shure, westone, etymotic, earsonic).
Full customs are also behind the 2nd bend.
I prefer the "behind the 2nd bend" type for isolation. The decibel attenuation is amazing.
Active noise cancellation is a bit of a gimmick to me and will not cancel as much noise as these can block.
Consider that ones that musicians wear on stage are "behind the 2nd bend".
Behind the 2nd bend is simply where it's at.
It Blocks out the bus, the inane chatter of idiots and most of the squeal of the skytrain.
It's how I ensure I stay sane during my morning commute. I sent my IEMs in to get repaired once, Showed up grumpy to work every day.
Instead of universal tips, I got custom tips done up, went to an audiologist and had impressions made then they ship them out to get molds made.
I went from dynamic, to double to triple drivers.
I'm never looking back.