My favourites are Pidgey and Ursaring, hence why they're my partners :/ Already explained why they're my favourites, so I guess I can just go with one of my other favourites.
Back in the day when I used to really obsess over Pokemon, back when FR/LG were still relatively new, I decided to go through a second playthrough of my Leaf Green. I had nothing planned out when it came to which Pokemon to use and such, so I just went along with what I found and wanted to use. I chose my Bulbasaur and went on my journey, (and oddly enough I didn't catch a Pidgey). I relied on my Bulbasaur all the way up to Mt. Moon, where it finally changed. I don't know why I wanted to catch it, since it was a Pokemon that never appealed to me, but for the first time I could remember, I encountered a Clefairy in there. I decided to catch it and try it out, and I wasn't really surprised. I realised I had a Moon Stone though, and evolved it into Clefable soon after (mind you, despite being a huge fan, I wasn't very good when it came to actually organizing teams and such), and it turned out amazing. I got to know it really well, as I went through nearly the whole game, through all the gyms and a few of the E4 members, with only my 'saur and Clefable. Even though I haven't used one since, I really loved it through that playthrough, with all the times it saved me, which is why it will remain at the top of my list.