God is perfect.
The English word
perfect comes to us from the Latin meaning "completion" or "fullness", and, indeed, in the earliest use in English meant to "to bring to completion or fullfillment." This is the sense used by the Greek philosophers and the early Christian theologians when they described the Supreme Being as "perfect", that in all of its qualities, it possesses them in the utmost sense.
But you are not alone; many, probably most, evangelical Christians also make the mistake in thinking that "God is perfect" means that God is the bestest in the whole world. But, as you point out, that makes no sense since "good", "best", and so the modern "perfect" is subjective and ambiguous. It is humorous (at least I think so -- but my sense of humor may be odd) to point this out to those who come in claiming that God is perfect. The problem with most fundamentalists is they don't even understand rudimentary theology. (Heck, most of them are heretics,
Modalists to be exact, but that's another topic.)
Rats and roaches live by competition under the laws of supply and demand; it is the privilege of human beings to live under the laws of justice and mercy. -- Wendell Berry