This isn't really meant to be offending but some Pokémon species are used quite a lot for original characters created by fans. Of course i don't really have a problem with that but it does get a bit repetitive after a while.
My list consists of the following:
1: Lucario
2: Gardevior
3: Lopunny
4: Kirlia
5: Eevee
I feel like I saw a lot of people do it as well when choosing their starter Pokemon while they were making their Trainer characters for the Pokemon tabletop games I play on other sites. I always tried to pick something that isn't seen very often. Once I had a Tauros as my partner Pokemon. Another time I ran a team of six differently statted Magikarp. And one time I went an entire game where all I ever had was a Pangoro and an Octillery. Between the two of them, I had a super-effective attack for anything.
If ROM hacks count, then I do recall Froslass being a very common choice for fan made Ice leaders. I probebly remember that because back when I documented my first Glazed run I forgot about Froslass and instead replaced it with Beartic.
I… might put something interesting here eventually.
Yeah Eevee is quite common, but it's incredibly cute so I don't mind it being popular. I also feel I see Espeon, Pikachu, and Vulpix fairly often! Piakchu's always been popular for OCs though if I recall?