Ohh god it has to be Zubat. Or rather, the Zubat evolutionary line. I'd always hate it how it'd make me hit myself almost all the time when I faced it (even worse against Golbat because of C-Ray; I think battling Agatha made me hate confusion for the rest of my life, lol), and then I'd use it and it'd be incredibly underwhelming. It was the same in my first runs on GSC of course, even though Crobat looked cool I just couldn't by arsed to actually level it up.
Then I went ahead and played my first game of Ruby (on my computer, since I didn't have a GBA), and I caught a green Zubat. Of course it was freaking ugly, but I was determined to make it work, so I even used the Steel Wing TM on it. Then, after a really rough time, I had a Lv. 29 Pink Crobat. Of course, it still wasn't amazing, but I really liked it anyway and gave it Fly :p . Afterwards, every time I'd play GSC I'd try to get Crobat even if it was annoying, simply because of how cool his design seemed.
I think I probably don't have that saved file because of how many times I had to format my computer, but that pink Crobat has got to be my favorite Pokemon. Even though its EVs were probably really messed up because I didn't even know how that worked at the time. I'm also not sure if it wasn't my first shiny, discounting Gyara of course, but it was definitely one of the first three, so that adds a few points, lol.
I still think RBY Zubat/Golbat has got to be one of the most retarded things ever, lol, but that's just my opinion.
Also that smiley is just stupid. Didn't realize at first.