The whole Porygon line, Nihilego, Lugia, Togekiss and Metagross!
The first bunch have all been big favorites for awhile; esp. Nihilego, it's my favorite gen 7 poke and I honestly considered using its name as my username on here!
Metagross has really grown on me ever since I found a shiny Beldum in Moon last year. It became a really fantastic team player in my VGC17 team, and I kind of just fell in love with it and its concept + stats + overall everything over the course of all my playtesting.