Just to add my (late) two round chips of copper:
I grow both species, and I have much better luck with ephippiata, beleive it or not. The inermis does grow faster, but, at least for me, the pitcher don't last very long at all. My ephippiata pitchers are very long lived, and even though it's not a speed demon gowing wise, it never has few than four active pitchers at a time. With the inermis, I'm lucky if one pitcher lasts long enough for the next one to develope.