This comes from the Google Analytics blog:
Can the Google Tag Manager snippet be placed in <head>? How about in my footer?
The recommended best practice is to have the Google Tag Manager snippet at the top of the <body> to maximize data collection, but some clients may find it easier to implement the Container snippet elsewhere in the in the page, like the footer.
Do not place the Google Tag Manager snippet in <head> (for the IT folks: this is because there is an iframe in the <noscript> case, which can have unpredictable results in some browsers).
No matter where you install the container snippet, you will need to make sure that this snippet of code is on every page of their site. Google Tag Manager will still work if you only deploy it on part of your site, but Google Tag Manager’s rule based system will only work on pages where the snippet is deployed. For more details, read our developer documents.
I think the best option is to install this in the Studio's Header section of your Skin.
Thanks,