Che's essay read with the most clarity for me and I enjoyed his writing style and his vision. Though Luxemburg's look at militarism was eerie knowing our current state and the history that followed her writing (and her tragic death at the hands of fascists), but her essay was long and repetitive, probably because it was originally published as shorter articles, so she had to keep repeating the same context she was responding to. Her prose was also just more difficult for me, though she's undoubtedly a brilliant thinker.
Marx and Engels are, of course, required reading for anyone interested in politics and the effects of capitalism, and it's arguably the most important text in terms of history, as so much conflict and revolution centered on this text's existence alone. It's not my first time reading it, however, so the other two essays interested me the most.