Sentret all the way :3! It's so adorable and how it stands up on it's long furry tail has always made me smile. The cheery looking personality it has also was one aspect of it I like. He can't only be a HM Slave, he actually served me well when I started playing SS a while back.
The others all look a bit ugly to me,especially Bidoof. Plump cheeks with ugly buck teeth? Ergh...not my thing to be honest D:. Rattata was alright but I still don't have much love for it along with Patrat. Those gleaming red eyes always kind of freaked me out.