Deluxe Prime is more poseable than Voyager Prime, that's for sure. I really like both, almost equally. Voyager Prime is the best in truck mode.
And the Earth Mode deluxe version, although similar in design to the Cybertron Mode deluxe, has a few new tricks and the clean look of the Voyager version in truck mode, so to me, that's enough to get all 3. And all 4, if you count the Roll out and command version.
