Direct Access to Model or to use Library?

[eluser]bunal[/eluser]
For example:

Lets say we have a user update form where users update their phone, email etc etc.

When user clicks the update form controller would?

1.Would it be better to call the model method and update the date

or

2. Would it better to always create a method in library then call the model method from the the library?

What will be your choice?