I personally would probably go with either a Pioneer or Yamaha from your list, as I think they usually offer the most for one's money, but it would also depend upon the particular deals I encountered. If the deal was right, Marantz or Denon would be fine, but I think they usually cost more for equivalent performance. The last two surround receivers I have purchased have been Yamaha, and I would not hesitate to buy another one, as they have been good.
I would not buy an Onkyo, because I like to be able to properly decode the old DPL that is on some of my DVDs, and unless they have changed their ways, they won't do this properly. You, however, might not care about that, as most people don't seem to (though most people don't seem to know how these things are encoded, so that could be part of it).
I don't like the looks of Harmon/Kardon, and they have, in the past, been somewhat irregular in their quality control, though they might have that fixed by now. But they tend to cost more than Yamaha and Pioneer, and I like the looks of Pioneer and Yamaha more, so there isn't any reason for me to select a Harmon/Kardon anyway.
I am sure that if the right people look at this thread, they will strongly take exception to some of my opinions. Ultimately, of course, you must decide what matters to you, and make sure that whatever you buy has all of the features that you require.
And don't worry; they will probably be able to dream up something new that everyone will feel the need to get, so it will probably be obsolete before you want it to be.
