I would think the Thompson HR ball would generate enough bidding to top the McGwire mark.
It certainly isn't the most expensive, but I saw where the ball used to give Derek Jeter his final strikeout reached above $1,000 at auction (not sure of the end price).
http://www.sportscollectorsdaily.com...-looking-sets/
He swung and missed at a strike in the dirt.
What I find interesting is that a ball that Jeter never signed, never touched, and whose bat never made contact with topped the $1K mark. I have a garage full of baseballs that match that description perfectly.
Tim