I like Wonder Trade. I got more than two boxes full of good Pokémon via WT. Some with perfect or nearly perfect IVs, some with egg moves or hidden abilities and lots that I just kept for the Pokédex. I basically got every starter at least once, some with their hidden ability (most of the time Froakie), a couple of shinies like Ariados, Eevee and a competitive Glalie and a few legendaries, including Hoopa, shiny Dialga, Regirock and Lugia, though the last two are most likely hacked.
I usually send off left over Pokémon from breeding (usually with at least 3 IVs), Pokémon with egg moves or hidden abilities or just relatively rare ones. I'd feel bad if I just sent off a common, weak Pokémon and got something really good in return. Besides, why would I go back to the first routes to catch random lvl 2 Pokémon, when I could just as well get something decent from a Friend Safari? In the beginning, when I hadn't beaten the game yet, I did trade some weaker Pokémon, but at least I slapped some items on them.