i tried both in my current poly~ looping project, and it turned out, that the komp is more cpu friendly (but not significantly). nevertheless i also found that the omx to my ears sounds better, it delivers a rounder sound, when you go from the presets in the help files and just refine them a bit.
especially for limiting i don;t see a way around teh omx limiter by the way. the komp set to brickwall limiting turned out to not be able to catch all peaks.
completely subjective, of course. i don't really have a mastering speaker setup here right now, so i might be soundwise misguided eventually.
One more thing to keep in mind, at least in analyzing differences between komp~ and omx.comp~, is the fact that omx cannot function at vector sizes of 32 and below. For people who depend on the scheduler for accurate timing, this can be a crucial DSP setting so komp~ would do better in such situations.