I've gotten a lot of competitive pokes from WT. Non-shiny ones, like Charmander, Drought Vulpix, Protean Froakie, Larvesta, Magician Fennekin, Gale Wings Fletchling, Squirtle, Snow Warning Amaura, Chinchou, and Ralts (later Gallade), all obtained at Level 1, which were all probably attempts to shiny breed. I have been EV training and leveling up every one of them.
I also have several perfect shinies from WT giveaways: Sylveon, Scizor, Jellicent, Linoone, and Arcanine, if memory serves. I also got 6IV shiny Virizion and Darkrai from WT, but have since given those away. (Idk, something about the combination of shiny AND legendary is ridiculous to me. :/)
I tend to hang on to WT breedjects, particularly females and pokes with their Hidden Abilities. Many of them already have egg moves and/or a few perfect IVs. These pokes become jump-starters for my own breeding projects. The perfect shinies also made parents for many of them, by virtue of their (typically) six flawless IVs. Every home-bred competitive poke I have has Wonder Trade ancestry.
This collection took me months to get. I tend to Wonder Trade my wild-caught shinies and my breedjects (competitive breeding leads to LOTS of leftovers!), and then Wonder Trade whatever I get for them, and on and on until I either get something awful that no one would want (so I can release it and save up space) or something useful that I don't already have.