My Milotic. When I battled Misty on SS and saw Milotic I just loved it. Then I tried every way to get a Feebas, and was determined to buy Pearl just to get the Feebas. I even played the game as fast as I could just to get to Mt. Coronet. Once I did I watched Youtube Videos, read on different Web pages and spent hours trying to get a Feebas. Once I did (I caught the two Feebas that popped up) I transfered it and went to Daisy for a week. Once it evolved... I can't even express my feelings. It wasn't shiny, but I spent such hard work on getting her, that she's my most precious Pokémon.
Right after her would be Latias. I spent almost 8 hours roaming all over Kanto to get her. My nephew was going to restart the game so I asked him to give me the Latias. I don't really use her but I would never trade her.
Yeah, neither of those are Shiny but I worked really hard on getting those two.