Moderator's note: Questions from new members using Asian English (with Hindi-based syntax), and often posting in the wrong category, have a nasty habit of being followed by 'helpful' links from other new members. (i.e. they're poorly disguised spam). If such a secondary post should appear here, I'll simply delete the thread. (I note that an identically-worded question has already been zapped from a different Q&A site, which makes me even more suspicious).
However . . .
If this is a genuine question it would help to know which program you're referring to! Photoshop? GIMP? Something else?
Assuming that it's Photoshop, the short answer is that the Pen tool offers greater accuracy but usually at the expense of taking far more time and 'fiddling about'.
See here:
http://www.bittbox.com/culture/basics-of-photoshop-quick-mask
and here:
http://www.bittbox.com/photoshop/pen-tool-tips-in-adobe-photoshop