My favourite is probably Pachirisu, it feels the most distinct to me, being more like a squirrel than a mouse. The white/blue aesthetic is nice, and the shiny is lovely. Plus for a time it was kinda meta relevant!
Come to think of it I don't think I've ever used any of them? Pichu is cute, I like Pachirisu, and Morpeko is really interesting. My favourite might have to be Dedenne if you made me pick? The fairy type and Cheek Pouch are probably what wins me over.
Pichu! :D It was my favourite Pokémon before Cherrim came along.
I didn't mind Minun and Plusle but their Do Not Separate vibe means I never really used them. I kinda like Emolga but the fact that basically every other electric type in Gen 5 is phenomenal, it also saw no use from me. The rest I completely forget about unless I'm physically looking at a picture of all of them together. u_u
Pachirisu is my favorite. I like squirrels. When I was a kid we had two tiny squirrels that could be kept as a pet at home. Thinking back about it now as an adult. I can't own a squirrel as a pet. They are better off in the wild enjoying their lives to the fullest. I can own a Pachirisu tho.
Dedenne is the perfect Pikachu clone. It still resembles Pikachu, it's cute, which fits the Kalos aesthetics and it's also a Fairy-type, which is a new type introduced in Kalos games, so it can showcase it. I also like Plusle and Minun. They are also cute.
My least favourite is Pawmi line. Especially the last one, Pawmot. It's cool to have another Electric/Fighting-type, but its design is so boring and ugly.