Maybe I can help you in this regard as it seems that we're in the same boat.
The things I was searching for in a good IEM (mainly for listening to EDM, rock and rap), were a good balanced sound with a "punchy" bass without being too "boomy" or "muddy", while still being accurate, clear and crisp, and having a good soundstage.
In my search for a good IEM, I first bought the Sony MDR-EX650AP because they are reviewed pretty darn good, and as a bonus there was a "try for 30 days" deal which enabled me to try them risk-free. While they have a "full" and clear sound, the bass was decent, but at the same time too "boomy" for me as it seemed to smother the music a bit. Overall they weren't bad, but they just weren't what I was looking for.
Shortly after I found a good deal for the Shure se215, so I bought them. They are accurate and crisp with a focus on the mids which make vocals come through very clear and up front, but they lack sub-bass and therefore lacking the "punch" that I like in my music, while having loads of mid-bass which bleed into the mids a bit which makes them sound a bit muddy, and the highs are rolled off too early to a point where they sound a bit "smothered". Even with EQing the lows and the highs up I couldn't accomplish a good sound coming out of them without them sounding bad. Overall the sound quality was better than the Sony MDR-EX650AP, but again, not what I was looking for.
Next up was the RHA MA750i. First off it needs to be said that these need a substantial amount of burn-in before they become pleasant to listen to, because right out of the box they sound horrible. The sub-bass is nice, but the mid-bass and mids are recessed up to the point that you can barely hear vocals, male vocals in particular. The worst of all are the highs, they just sound harsh, "metallic" and a bit sibilant. When I listened to the MA750i at first, it even made me feel unwell....
With the bad points of how they are right out of the box out of the way, here's how they sound to my ears after 70 hours of burn-in and usage (my burn-in goal is 200 hours):
The sub-bass sounds even slightly better (DEEP and lush), the mid-bass and mids have come more forward, although still very slightly recessed but now to the point that they sit well, which in turn made vocals come forward too, and the highs have settled down quite nicely as they are no longer sibilant or too harsh. With that said, the highs are still very present, but luckily the MA750i handles equalisation very well (it also accepts EQing the lower frequenties up very well if that's what you wish), so EQ'ing the high frequencies down without losing sound quality makes all the difference and it makes them very pleasant to listen to. What I've basically done is look at the frequency response chart and invert the peaks in the high frequencies down (3kHz - 6kHz and 9kHz - 16kHz).
In conclusion, to me, the RHA MA750i beats the MDR-EX650AP and the se215 HANDS DOWN, but only after giving them a proper burn-in and EQing the high frequencies down a bit. The soundstage is excellent, they are accurate and crisp. Also when it comes down to comfort, I personally like the MA750 better than the se215. Yes, the ear-loops of the MA750 are not as stiff and malleable as the ones on the se215, but the fit is better and I don't even notice them sitting in my ears.
If you want to follow the progression of the burn-in process that I'm giving the RHA MA750, have a look at my thread:
http://www.head-fi.org/t/823494/need-iem-advice-dont-know-what-to-do-anymore