My favorite is Crobat
I love the design of crobat, and Crobat and i have a bit of history...
It all started at the My very first game (leaf green) and i had just bested Brock, and was entering MT. Moon for the first time; 1st poke zubat, 2nd zubat, 3rd geodude, 4th zubat, and the fifth; was a shiny zubat! Of course i caught it, and it stuck by my side for the longest time. I leveled it to 100, along with my other Pokemon on my team
and even moved it to newer games like Diamond. (where like all the other Pokemon in the game died) game broke)
And during my first playthrough of PokeMMO the fifth poke (at MT. Moon) was a zubat, and i caught it for good times sake; and I later found that this was a competitive zubat. with adamant nature.
So yeah when i catch zubat's for actual use; i name them Yogurt, in memory of the shiny Crobat i had when i was a kid.