There are pros and cons to both. I owned the XBA-4 and IE8, and have auditioned the IE80.
First of all, the IE8/IE80 do not have very good isolation and can be a little difficult to fit. If you plan on using them on the go, the IE8/IE80s might not be ideal for you. For example, they didn't isolate enough on my train/bus commute.
Another potential issue is the XBA-4 (non-mic version) has a very short J-cord. This is the kind of niggling thing that can be annoying, as they are quite short without the included extension, but quite long with it. For me this wasn't a problem because I always put my iPod in my shirt pocket.
And getting to the sound...
IE8/IE80: Amazing soundstage, excellent and hard hitting bass, sparkly treble, and smooth though slightly recessed mids. The IE80 isn't a huge sonic upgrade of the IE8, but does seem to flatten out the sound a bit and reduce the infamous mid-bass hump of the IE8. Overall, a very warm, full engaging sound.
XBA-4: Punchy, well-extended bass, smooth mids (more forward than IE80) and well extended though slightly grainy treble. The XBA-4 has an overall cleaner, more articulate sound, particular in the treble, where the grain can make it a bit more fatiguing. While BA earphones are usually known to be more detail-focused and bass-shy, (or to some people, "boring") the XBA-4 has a fun and engaging sound.
My pic of the two would be the XBA-4, because it is better suited to on-the-go use and I like the level of detail. For rock it is particularly good. The IE80 is definitely a bit smoother and probably a better choice for electronic/hip-hop.
Edited by takoyaki7 - 4/13/12 at 7:38pm