It's really just your preference, however, greenaddress does offer better security and features. Greenaddress allows you to setup a transaction limit and will limit your transaction volume. If your account gets hacked, the hacker will not be able to make more transaction than what you specified. Also, blockchain.info has some security holes before.
Yes, it is 100 time more secure than blockchain.info - check the greenAddress official thread here in the forum :
https://bitcointalk.org/index.php?topic=521988.0I couldn't find an option that lets user have control over their Private keys, what happens if for some reason the site is down? How will a user get access to their funds?