Unless you have a specific application in mind for the the WiFi in the 2nd Edition (which isn't very useful in general), I suggest going with the Book Edition.
The largest font size on the iLiad is significantly larger than on the Kindle, see
Things you can do with your iLiad. The 1st screenshot is FBReader and the 2nd the MobiPocket Reader. Note that by default there are only two fonts available for MobiPocket Reader, see
Mobipocket Font Switcher.
To read most ebooks on both the Kindle and the iLiad, you will need to strip the DRM from AZW and/or MOBI. FBReader (which only reads DRM-free ebooks) may then be a better option than the standard Mobipocket Reader on the iLiad.
I assume you are aware of the issues with the iLiad, primarily a slower page turn than most recent devices and only a ~12 hr battery with no suspend mode.