I am just wanting to fire an event to GA on the submission of a form. What is the best way to do this? If possible i would like to use Google Tag Manager to do it.
@Max S I would not advise using a dumb event listener that may think any submit button click == successful submit.
The only way to get a proper accounting of successful submits that pass validation and reach the Marketo servers is to use the supplied onSuccess event.
With Google Tag Manager, you can setup listeners that tracks Form success on any page GTM is installed on. You can then use that as an event in Google Analytics, or any of the other tags installed.
I'd do any followup calls in the onSuccess handler because that way you are logging a successful form post, rather than just an attempted one as in onSubmit (not that failure is common, but it's the proper way).