Is PieFed "better" than Lemmy in the sense that there is more / different content? It looks like there are distinct / different posts when I browse it.
In theory no, they should both have access to the same content. Are there any examples of posts you see on PieFed but not Lemmy?
There are a bunch of reasons that come to mind. Sorting algorithms are different, for one, so you may see different posts even if the same ones are on both platforms. Secondly, PieFed has some powerful set up functions that allow you to pull communities from other instances or from the lemmyverse.net/communities list, rather than needing someone to find and subscribe. PieFed also recently scaled up it's mastodon integration, so now there's a "Microblogs" community where mastodon posts go if they weren't posted to a lemmy community, which may be content not available from Lemmy.
You can ask questions about the Lemmy.nz instance here.
This community also serves as our Meta community, with posts about updates to the Lemmy software on Lemmy.nz or other things relevant to Lemmy.nz users and not relevant to other instances.