IEM's for me. But I think it's more appropriate to say that they're just different. IEM's just have this "intimate" sound that full headphones can't match. Maybe depends the music you listen to. I listen to a lot of vocal-centric music, so the feeling I get when it sounds like the artist is actually right there singing next to me made the decision for me. However, in instances when I listen to metal, full headphones hands down win. The imaging and soundstage make that kind of music. So just depends the music you listen to.
Also, the portability. And the physical feeling. When I wear full-sized headphone I feel like I have a helmet on. IEM's just disappear.
My audio journey: CX 300 --> CX 985 --> Over-ear Momentum --> V-moda XS --> SE846
I went up and then came back down (with full force) once I realized that IEM's are the headphones for me :)
So the SE846 just sounds better than the Vmoda XS headphone? that's why you went back to IEM? or?
Im on the same boat, right now im trying to decide if i should stick to my $700 iem , or just a decent $200 headphone :( it's so hard