Both Gardevoir and Gallade are good on your team. You might choose Gardevoir because it is hard to get a Dawn Stone during the game (just as Tadpokenerd said). It is better on the special side, but has a crippling defense base stat about 65. It doesn't even improve when you mega-evolve, so you would have to be careful around Physical Attackers. Normal Gallade seems to have around the same defenses, but M-Gallade tends to be more bulkier as it has 95/115 defenses and is a physical attacker. It all depends on which one you think is better. As I said before, Gallade and Gardevoir both are solid choices.
Personally, I would suggest Gallade. But you can decide for your self here:
As for Ducklett, I have no suggestions because I hadn't played it yet :P.
I hope this helped!