I like my covers to relay an "idea", not a whole story. So my tastes tend to be somewhat in the middle. Moejoe does great work, and as for his suggestion for the logo for Earthfleet, I love it.
His suggestion of consistency also works (ie, I'm sticking with simplified space scenes that relay a key idea from the book) and I've been trying to follow it, albeit loosely.
And you know what? I think moejoe just sparked an idea in my head for the cover of book 5! His Earthfleet logo he posted, on an all black background (or maybe a field of stars) would make the perfect cover.
Now I just need him to help me put some spit and polish on the other two covers.