Pidgey line - I just love their designs, what can I say?
(Unlisted) Spearow family - I also really like these guys too, they don't get enough love :c
Meowth line - I really like Meowth from his appearance in the anime :P
Eevee - Absolutely one of my favorites <3 It's super adorable, and it's evolutions are amazing, I believe nothing really more can be said that hasn't already been said :P
Porygon line - Just love its design and interesting moveset.
(unlisted) Jigglypuff line - They're adorable, and I like Jigs' appearance in Smash :P
Tailow line - Like I said in the Flying poll, I used it a lot in Emerald and AS
Zangoose - Just think it has cool design.
Castform - He may not be reliable competitively but I like his design and concept :P
Starly line - I have a thing with normal-flying type birds :P
Arceus - Love it's design, and it has a pretty badass story to it too
Cinccino line, Meloetta, and Helioptile line - They're just so adorable :D
Other ones I like are Fletchling, Girafarig, Furfrou, Lillipup line and Deerling :)