They're all the same game version as the free one, there's just a few little bonus rewards at certain donation levels.
$5 gets you a SFW wallpaper set (6 pics)
$10 gets you early access to future updates (~1 week)
$15 gets you a NSFW wallpaper set (6 pics)
Like I said, they're just little thank-yous to those who choose to donate <3