I'm grading based on skill and word choice, not to mention entertainment. It's clear they both have been doing this a while, but Nimbus seemed to be grasping. I don't know why others seem to think the "punches" are hard-hitting, they're just filler lyrics that had to reference his name. Then a Fosters/Outback reference because of apparently being in Australia? Either he's dumbing down his cultural awareness to appeal to the young NG crowd, or he's just lazy. Oh yeah, and it had to rhyme. His flow is good, for sure, but beyond that I wouldn't rate it.
After following the competition and reading about Nimbus' past, it was pretty obvious PiGPEN would go after that. I prefer the more personal attacks, mocking of style, and homophobia parodies. And anything with Groundhog Day gets my attention. Saying "reference" twice annoyed me though.
Again, they can both rhyme words well, but when it comes down to lyrical content, I'd take PiGPEN.