What is the best way of customizing SharePoint List forms(NewForm, Edit form, Display form).
- Application page - object model
- Visual web part - object model
- SharePoint Designer 2010 - ECMA script
Which one will be the test for site level backup?
You have many "good" ways to accomplish this. If you are looking for a replicable way of doing this, using a custom Visual Studio solution would work best.
If you are looking for a way to do it on a single list, you could do it with SharePoint Designer or with InfoPath Designer.
With more details, we could provide a better recommendation.