I have both the K3003 and the FitEar TG 334, and I find both are exceptional in their respective ways. The former is airy and pristine, rendering instruments---and the human voice especially---in such a way as to bring out all their subtle nuances. Details are emphasized but not overbearing. In this sense I'd say it's more of a hi-fi type of device with a definite wow factor. The FitEar by comparison ranks as one of the most, if not THE most, transparent IEMs I've ever heard. It's exceptionally accurate but slightly more sedate in comparison to the flightier K3003, and in that sense I'd say it's a reference device first and foremost. Though both are great for reference listening. The presentation is slightly more restrictive with a bit less breathing room on the TG 334 I find. The K3003 seems more expansive. On the other hand, imaging seems more accurate on the TG 334 and objects within its space are more clearly delineated.
To overgeneralize, the K3003 strikes me as being the more obvious "fun choice" between the two.
It's also worth mentioning Final Audio Design's FI-BA-SS, another contender vying for the title of "top universal IEM."