The best packer is none. No speed kills, size increases, compatibility issues, virus detection issues etc... Perhaps UPX might suffice if you want to get your file size down, but according to others Combat Arms shuts down if a UPX'd app is injected into it.
What are they going to do with your hack? Get the addresses of it which will last 2 weeks?
Microsoft Windows, Microsoft Office, Zune, iTunes are unpacked, fyi.