I've tried Audio Technica CK100, and about to try the Ortofon e-Q7.
If you listen to hip-hop and rock, the CK100, may not be the best choice. It excels, though, better than any other universal IEMs with its mids and highs...in particular, j-pop/j-rock. From talking to some other head-fi members who have tried multiple high end universal iems, they would agree that the CK100 cannot be beaten with that category.
However, the Ortofon seems to do better in all other categories than the CK100, with bass (quantity i believe) better than CK100, and mids being about the same and highs a little less detailed than the CK100.
The sennheiser IE8 should have the largest bass impact, but again, I don't know too much about these ( I just read about them). I believe they go well with electronic / trance music.
Lastly, I won't comment on the SE420 since I have not read much about it or heard it before.
Cheers
P.S This thread should not be in this section of the forum.