Well, an argument can be made for all of the cameras you mentioned. I myself shoot with an S2, for at the time I was getting the most of what I needed out of my digital camera with that model. Now of course there are things like the 10D and SD9s etc.
I would say if you have no lenses and arn't sure what you wanna do in the long run go Canon to start. Great things at great prices.
this much i am certain, you can buy all of these cameras at Unique Photo Inc.
so just drop me a line (firstname.lastname@example.org or call 1-800-631-0300 ext 292) and I can give you a quote on some digital cameras. For what its worth, currently we are offering the D100 with an EXTRA battery, and we all know what those Nikon batteries go for now a days.
Your Local Unique Photo Counterboy