iTunes Helper is no longer shown as a login item, so the technique of removing this to keep iTunes away no longer works. However, there is an ignore-devices
configuration value to tell the helper to stop launching iTunes when a device is attached.
Set this option like so (seems to take effect immediately):
defaults write com.apple.iTunesHelper ignore-devices 1
This allows you to keep auto sync enabled in iTunes (so it will sync when you decide to launch it manually), while also keeping iTunes from still popping up when your device has a software update available.