Any order works well as long as you get out of the major cities and out to your "wilderness" areas" fairly quickly. I think flying into Argentina and immediately going to Uruguay (less "wilderness" there, then on to Iguasu Falls, then take the road over the mountains through Mendoza to Chile and head on north cutting back through Paraguay, Bolivia, Ecuador, Chile, Peru, over to Brasil (Brazil), then back to Columbia and Venezuela, and on north to Panama, Costa Rica, El Salvador, Honduras, Guatemala, finishing in Mexico.
Like you said, I'd skip Guyana, Surinam, and French Guiana. Not much in those places compared to many of the other countries;--and to be blunt, you'll be way short of time even trying to see all of these other places.
One last thing--be aware that the roads between Columbia and Panama are essentially non-existent (see the following web link: http://en.wikipedia.org/wiki/Dari%C3%A9n_Gap, so plan on taking either a boat or flying between these locations. Also, going over the Andes from Peru to Brazil via road is difficult--and then you will be in the middle of the Amazon jungle, so you may want to fly to Rio also.
[ Edit: Edited on 21-Sep-2012, at 07:54 by Calcruzer ]