[jQuery] find form from input?

Let's say i have this construction:
<form>
<fieldset>
<legend></legend>
<input type="text" class="textField" ...>
</fieldset>
</form>
And i have this query
$('.textfield').each(function() { ... });
How do i find the parent form?
a) jQuery('form').contains(this);
b) jQuery(this).parents('form').. ?
What is the best and fastest way?