I often send out legendaries I don't need, wormhole shinies, and breedjects. I've gotten a shiny Rapidash, shiny Staryu, and shiny Nidoran (F), as well as a Phione and tons of high IV/hidden ability lovelies.
I've gotten a ton of stuff thanks to WTW. Mostly garbage, though I have gotten a few Pokémon with good IVs and/or in rare Pokéballs. So far the only shiny that I've gotten though it is a Lunatone (which also happens to have perfect IVs).
Crazy wonder trade stories! -I got a shiny Mawile that wasn’t hacked -I got a hacked shiny Pidove -I got a level 81 Japanese Solgaleo holding a poison barb -and also hundreds of Poochyenas and Zigzagoons
I did a ton of Wonder Trading. I mostly got common stuff but among them was: -A shiny Swampert -A shiny Happiny -A shiny Victini -A shiny Genesect The Victini and Genesect were both hacked though. Victini can't be obtained shiny and Genesect was available shiny through an event a long time ago but it had a fixed nature and the one I got didn't have that nature.
My favorite WT moment was when i accidently wondertraded with Hrae while I was talking to him. Gosh, that was so funny
A Shiny Mewtwo. I was randomly trading away extra HA good-IV hatches I had since I prefer to instead of just releasing them, but then I came across a Shiny Mewtwo (this was when XY was still going strong) and it was honestly one of the only shinies I ever got in WT. (Later traded it to a friend who always wanted a Shiny Mewtwo, but now I have a Shiny Vaporeon instead, so it's all good.)
I've gotten a few Lv. 100 shinies, they're probably hacked but hey I don't have to do any of the work. I also got a Lv. 100 Garchomp with a mixed moveset and all the right IVs and nature needed to be properly used. Best and most hilarious moment was still when I traded with Morg while we where doing WTW. I also got a mon back I bred and hatched, I remember it because it had the name indicating it was from out WTW events.
I really don't like wonder trade, but I tried it out a few times when XY came out. I got a shiny Pokéball vivillon when it wasn't obtainable yet even in its non-shiny form. ...That's why I don't like them. At least for now.
The first really good Wonder Trade experience I've had is in Pokémon Y when I sent out a really low-level Surskit and got in return a lvl 100 shiny Giratina. I treasured that Pokémon for a long time and still love it and Wonder Trading to this day