I much prefer the hPDA for daily notes and Next Action lists. This is mostly because a collection of note cards can be reordered based on priority and current context, while a Moleskine's pages are locked in place.

This is really geeky, but I use a Buxton Note Jotter for my hPDA instead of a binder clip. (Those photos aren't mine, but that's the thing I use.) The best thing about the Jotter is that it's sturdy enough to act as a writing surface, plus the front "viewing window" always has a fresh card available for taking notes and capturing thoughts whenever the need arises. I use unlined 3x5 cards in my setup, keeping a few unused ones in the viewing window, the used but unprocessed cards in the first pocket (along with receipts, basically a "mobile inbox"), and my Next Action lists (one context per card) in the second pocket.

I also have a couple of Moleskines, but they're not carry-everywhere sorts of things. They're really great to write in, but they're not very versatile and they end up being filled with things more "permanent" than the constantly-refreshed cards in my Jotter. Ideas from focused brainstorming sessions, snippets of music I'm composing, and other "serious work in progress" gets recorded in my Moleskines.

Oh, and by the way... read GTD. For a while I thought I "got it" by absorbing online comments about it, but I was never able to create a system that worked until I actually read the book.