I have been reading about Angular2 new Forms API and it seems that there are two approaches on forms, one is Template driven forms other is reactive or model-driven forms.>
Reactive forms:
Template-driven forms:
In summaries, if forms are very important for your app, or reactive pattern are used in your app, you should use reactive forms.Otherwise your app have basic and simple requirement for forms such as sign in, you should use template-driven forms.
There is a angular offical link