That's easier then...
The first thing to note is none of your listed devices will be suitable if a digital camera replacement and a Creative Zen replacement are two of the key priorities.
The iPhone, Pre and the Hero will easily replace the Zen, but not the camera which is reasonable, but never going to replace a standalone, even an older one.
The Bold wont offer as good media playback as the other three and it's camera is average at best. This is a great messaging device though.
The N97 is best avoided on all counts, IMO.
For media playback and camera quality, the Nokia N-series (N86 etc) are a very good choice, with the exception of the N97 as mentioned. The Sony Ericsson Satio is another fine choice. These lack the internet browsing abilities of the iPhone and Hero though and are OK for a quick Google search of mobile versions of sites at best. Nowhere near the full internet though.
My advice is there isn't a camera phone on the market that can truly replace a standalone digital camera for all your needs. Many take very good daytime shots which will be fine for most purposes, but they still lack the detail and accuracy of standalones.
Media playback is easier, most smartphones do a very good job of this, so no worries there on any device mentioned so far.
Internet browsing, given your requirement for the full internet experience, is best left to the iPhone and Hero (or other Android device) - I'll comment on the Pre when I get my hands on my loan device shortly. These really are the best web browsers around and few others can match the overall experience.
So again the only way to make a firm choice is to work out your exact priorities in order and work through each device in turn. Sadly if unsurprisingly there isn't one device that is the best in every possible area, which your wish list covers.