Which level 7 creature is the best, and why?

Oh, well, if this is just a topic about preferences... I like the demons because they are well-drawn, their movements and burning animations are cool, and the way they beckon with their finger is great! As for the stats... it all depends on the situation. And the art lies precisely in having a level 7 unit (and other levels) appear at the right time and in the right place, using it as effectively as possible.