Let me throw another opinion on the fire.
1) I much prefer the Standard icon set. I find it more distinct and easier to distinguish at a glance because of this. This just means it is less work for my brain and eyes to use it.
2) I think we should honor the wishes of the pro-Tango camp and make the Tango set default so that we can do our part to promote greater platform consistency. I believe this is a greater good even if my personal tastes differ.
3) I think requiring the user to find and rename files to change the icon theme is completely out of line. We should have a gui icon theme selector in the preferences dialog. And I think this will make the choice of default icons much simpler because it will be easier for people to discover that options exist and test them.
Aaron Spike