if you need moaarrr bass than S4 go with monster turbines or if you need quality bass go with Radius DDM / DDM2, i have used both turbines and DDM and i love DDM more
My journey with bass rich IEMs have been like this
Creative EP830 > Meeelec M6> Sennheiser CX800> Brainwavz M2 > Klipsch S4i> Monster turbines > Radius DDM > UE TF10 and finally lost the zest for bass cos of promotion at work and lesser listening hours had to come back to brainwavz M4 coupled with my note2, had to sell all my sources (Ipod touch 4g + Sansa fuze + cowon d2) and all IEMs above
It again depends on one's taste and genre i used to like DDM / TF10/ Turbines more on classic rock , hard rock , 80s , vocal trance , AOR , glam metal and some heavy metal
now that life seems more sane to me, maybe ive managed to find a balance between personal and professional life , ive decided to continue my journey with IEMs Planning to go the IE8 way , gonna order em soon via Amazon as i dont find new ones available anywhere else, IE80 to me seem very overpriced