i have got brainwavz m3 and heard both se215 and s4 and in my opinion m3 betters both of them
se215 is the best value due to its detachable cable,super comfy fit and overall build quality alongwith good sound.
s4 is very bassy although bass is not tight with recessed mids
m3 has the best balance in terms of sound as well as clarity.
that was my opinion,,,,,,,pls share ur experiences