SE215. I used to own the turbine; the bass wasn't enough for me. It was punchy and compact, but didn't have the real wow-factor that the SE215s pack. Neither are a true basshead IEM, IMO, but even though the Turbines have better overall SQ and detail, the SE215s win on fun factor. The turbines were just boring to listen to; the SE215s really sound alive.
I would say the areas in which the SE215s surpass the Turbines objectively would be the warmth and forwardness of mids, the quantity of bass, and soundstage, but the highs can sound artificial sometimes. The Turbines are objectively superior in that they are more detailed and clear, and have better all-around quality and detail of sound, especially in the highs, but the bass is less than often claimed and requires a perfect seal to come through, and the whole sound is generally rather boring IMO.
My personal preference is for the SE215s. They have an awesome "fun" sound and just the right amount of bass for genres like trip-hop and house that ask for bass emphasis but not huge gobs; they sound good with dubstep and trance, too, and you do get some nice rumble with them (which the Turbines were not capable of, at least IME) with the right tracks and maybe a touch of EQ.