When should I use Custom Fields or Form Questions?
Both types of questions are made for the collection of demographic data. For example a name or an email address. But both differ.
Use custom fields when you want to automatically insert data in your survey or quiz. Ask your respondents to follow a link that already includes some extra data. E.g.: "su.vc/quiztitle/?cf1=TeamA". In this case “TeamA” will automatically be shown in the intro screen as one of your custom fields. In the results pages you will be able to filter/visualize data based on this custom field (e.g.: I only want to see the results for TeamB). For more information about custom fields please read this article.
If you want the respondent to leave his contact data (for example by presenting a tablet during an event) then you better use Form Questions. Several formats are available: email, date, drop down menu, numbers, text area, opt-in.