Notice any similarities between those two? The types are almost the same, the stats are almost the same, and the support movepools are almost the same. And, their tier is the same. NU. However, I belive that these Pokemon can have great success in OU.
Gallade is more of an offensive Pokemon, with Swords Dance and a variety of physical moves. As such, his Swords Dance set can work well.
Gallade @ Life Orb
4 HP/252 Atk/252 Spe
Ice Punch/Stone Edge
Gallade also has deadly defensive options just like his sister, Gardevoir, but she pulls them off far better.
Gardevoir is more defensively inclined, with useful support moves such as Will-O-Wisp and Hypnosis to make use of. As such, a special tank set is obligatory.
Gardevoir @ Leftovers
252 HP/4 Def/252 SpD
Hypnosis/Protect/Heall Bell/Trick Room
Gardevoir has many, many other options, including but not limited to Trick Room, Dual Screens, and Memento. Gardevoir also makes a great weather counter due to her decent Speed and Trace to counter any Chlorophyllers or Sand Rushers.
There are many other ways to use these two Psychic types, but I do not know of them. Discuss these two Pokemon, and the future may be brighter for them.