Some Things to Consider
I've used NeoOffice for several years, but have not yet upgraded to Version 3.0, which has been in beta for a while. I have also tried OpenOffice.org 3.x for Mac OSX. I love some things about Pages and Keynote in iWork. So I have perhaps an unusual perspective to offer. But I'll try to be brief.
As for Neo vs. Open, for me the primary difference relates to integration with the OS. Neo is much more cleanly and seamlessly integrated. Things like Spotlight search, Address Book, spell-checking, and access to Mac Services are included in Neo, but not (at least yet) in Open. Because Neo is essentially its own fork of Open, it doesn't have to do things just so the code base will continue to be compliant with other platforms and i find that often makes enough of a difference to continue using Neo.
While it is true, as someone said earlier, that both Neo and Open take a while to load, the load time isn't any slower than would be the case if you simultaneously opened, say, Word, Excel and PowerPoint or, for that matter, Pages, Numbers and Keynote. And you only have to load once, so I find that sort of a non-argument for the way I work.
Pages, Numbers and Keynote are far and away the most Mac-like of the office "suites" (though it is not strictly speaking a suite). That's the Good News. The Bad News? Pages, Numbers and Keynote are far and away the most Mac-like of the office "suites." That means they work almost nothing like any other office productivity tool you've ever seen or used. While I really, really like Pages a lot, I find that for anything other than fairly simple documents, I spend too much time trying to figure out how to do things than doing them. If you aren't already steeped from decades of ingrained practice in one of the more standard interfaces, I'd go for the iWork tools. They really are good. But if you're an inveterate user of Word or Excel or Powerpoint or their Neo/Open equivalents, then you might find yourself really frustrated trying to learn their iWork relatives.
BTW, I do a lot of moving documents between Neo and Office formats in both directions and very seldom run into a conversion issue. The same is decidedly not true of Pages, whose support for Office is marginally adequate but unfathomably bad at some points. The same is not true of presentations: PowerPoint back and forth between Neo and Keynote generally works very well.
For me, Neo keeps on doing the job with a very good implementation of the MS standard as adapted to OS X. Support has been excellent (better now if you pay $25 or more in donations, which is strange but inevitable) and the community is absolutely first-rate.
I'd be happy to answer other questions if you like.
