Who does the best body kits/parts?

NorthStyle

The carbon 3-piece lip (I'm assuming V2 Nismo) and side extensions are available from Carbon Signal. Next Level Performance is a vendor/importer for them. Their fitment can be great or not-so-good, but generally decent. Fly1 make a rep buuuuut they're fitment is all over the place from excellent to atrocious (I've heard more bad than good and I've never heard anything positive about their customer service if you're outside of their local area, so I'd strongly avoid).

The rear "diffuser" (I'm guessing the Street Aero by the description) I've heard mostly positive. It's not a functional diffuser, but if it's the look you want then you should be fine.