OK let me carefully lay out my thoughts
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IE8 has the largest sound stage and the most bass (often to much especially in the mid-bass), I found the mids to recessed and influenced by the bass, and found the treble also not to my liking (to tinny sounding when it came to cymbals in particular).
MTPC has a much more intimate soundstage (smaller) the 2nd most amount of bass, midrange was warm and full on one pair I owned and slightly recessed and thin on the other pair, treble was nice and sparkly and reproduced cymbals well but would occasionally become to hot,
SM3 has an unusual soundstage in that it places you in the center and can have a massive stage all around you depending on the recording (good for some music but wierd for alot of music as well), good bass for a BA but does not compare to any of the dynamic based IEM I'm talkng about, has warm incredibly detailed midrange that is quite forward, treble seems recessed and often even veiled.
SE215 has almost as good a soundstage as the IE8, the least amount of bass of the dynamic IEM's listed but still has good sub-bass and only a hint of a midbass hump, mids that are close to the SM3 but not quite as forward, treble that is slightly recessed but clearer than the SM3 and the IE8 with good cymbal reproduction.
In terms of detail I would say SM3 > IE8 > MTPC = SE215
In terms of build quality I would say IE8 = SE215 > MTPC >> SM3
In terms of comfort I would say IE8 = SM3 = SE215 > MTPC
In terms of fit kit and accessories I would say SE215 = MTPC = IE8 >>> SM3 I have to say that while IE8 has the largest amount of stuff followed by the MTPC I found much of those items simply didn't mean anything to me especially in regards to the IE8 stuff. The SE215 on the other hand while having less stuff is a good selection that would meet most peoples needs. The SM3 on the other hand simply does not give enough in their kit.
So taking everything in as a whole I would say while the SE215 while not winning in many areas is near the top in most areas and offers a compelling argument as being as good as any of the others considering it does not have any major weaknesses. If you take into consideration it's price point it's a clear winner for me.