It took me a while to determine an actual favorite. At first, I just went with the flow and accepted Pikachu as my favorite -- it was everywhere, after all. However, that changed after I beat my "gaming god" of a cousin with a Ho-Oh (not even lv90, mind you) on Pokémon Stadium 2. (He was using Legendary Pokémon as well, including Mewtwo, all lv100.) I hadn't defeated Red in Silver at this point, but my cousin suggested that I could probably take him down with my team. Sure enough, I was able to do it. Both of these points combined made the rainbow turkey my first actual favorite.
Years passed and I started thinking more deeply into the aspect of favorite Pokémon. What ARE favorite Pokémon, anyway? Are they Pokémon you like because they're strong? Are they Pokémon you think are cute? Are they Pokémon that bring back memories and you like them unconditionally, regardless of how strong/weak they may be or how they look? Sure, Ho-Oh's cool. It's strong. But is that really how one would or should go about determining a favorite?
One day, Christmas day in fact, I decided to see what Pokémon were swarming on Pearl Version. It was Dunsparce.
Now Dunsparce is another Pokémon I had spent some time with as a kid. Ever since seeing it in Beckett Magazine, I had assumed that it evolved into Gligar (since they're listed next to each other in the Pokédex). When I finally got Silver Version (my first Pokémon game) and encountered one of these rare and bizarre Pokémon of my own, I trained it -- a lot -- trying to evolve it. This obviously never happened, but I didn't stop there. Pretending to be a "Pokémon Professor" of sorts, I recall drawing charts and such noting the similarities between the two Pokémon, like their wings and stinger-tipped tails.
I'd never had any luck with the Poké Radar before, but I suddenly felt the need to have a Shiny Dunsparce in my life. On to Route 208!
And that was my first successful Poké Radar hunt. I didn't even use Repels and managed to get a "Shiny patch" at a low chain of 14! (This wasn't my first Shiny Pokémon ever, but it was the first that I was intentionally looking for.)
I didn't start training "Noko" right away (I wanted to wait until HGSS came out so I could replace my starter with it), but it was right around that point that Dunsparce became my new favorite Pokémon. My fondness of the lil' guy just blossomed more from then on.