The most advanced units are obviously part of the Metric System.
To be honest, the English system is more of a series of apparently unrelated units somehow
very loosely based on a duodecimal system.
And as an American student of science, I am willing to admit to this.
Stupid [whoever], ruining unit conversions for the rest of us

.
To be fair, there are some quite fair uses of the CGS system, which has some potentially very magical advantages.
Amd I'm not even sure how Slayer's music factors into all of this.
At any rate, I forgot what you were asking since I am far too busy headbanging.
In game, the Lucy Suit/Tyrant are technically the most advanced. But that doesn't mean they are the most useful. Or the most sober.