
ziphone changes the bootloader PERMANENTLY whereas Liberty+ uses a fake bootloader to trick the Iphone that is reversible if necessary. If for any reason you need to return the iphone to Apple they will know that you used third party software if you use ziphone which will void your warranty. If you use ILiberty, you can restore the phone to it's original state so there's no trace of jailbreaking thus keeping your warranty intact.
Pwnage will do the same job but many of the third party apps won't work on the 2.0 firmware yet. Unless you can write your own apps, I would suggest to stay away from pwnage and use Iliberty+.