Which third-level creature is the best?

Well, in many situations, yes, but sometimes you need units that can move around quickly.

But units designed for running around are different (although towers don't really need to run around much). And having a unit that's "a jack of all trades" is too good; only level 7 units can boast that, and even then, not all of them. In general, there are no truly universal units in the game (which is a good thing): either they defend well, or they move quickly, or they shoot well, or they fly, or they can do several things, but not as well as "specialists" in each skill.