"Insert the asynchronous snippet at the bottom of the <head> section of your pages, after any other scripts your page or template might use. [...] We've determined that on most pages, the optimal location for the asynchronous snippet is at the bottom of the <head> section, just before the closing </head> tag."
It doesn't really matter much when it comes to Autoptimize, but according to Google, the asynchronous code should be put just before </head>. From http:// code.google. com/apis/ analytics/ docs/tracking/ asyncTracking. html :
"Insert the asynchronous snippet at the bottom of the <head> section of your pages, after any other scripts your page or template might use. [...] We've determined that on most pages, the optimal location for the asynchronous snippet is at the bottom of the <head> section, just before the closing </head> tag."
Please report back the results of your testing :)