Like tails first or pins first, the paddle and pin versions of the DF500 have their pros and cons.
Paddles, e.g., have these pluses:
"The new included Domino fence, which can be purchased separately (495 348), is backward compatible with existing Domino joiners and features square stop flaps which offer improvements over the previous round pins. The square stop flaps are less likely to get caught unintentionally in adjacent mortises and are less likely to be affected by glue residue."
But the pins allow one to register the machine at an angle on narrow pieces to make angled mortises (think: louver shutters).
To say one version is always better means the full potentials of the machine have yet to be explored. (For hand tool users who insist tails are better: some dovetails can only be cut with the pins first.)
I heard that (not sure about its accuracy) the pin version was withdrawn because of some patent infringement related issues. The best version, to me, is if we could have a DF500 that gives me the option to use either of them.