Bug - Butterfree, they look absolutely adorable and the butterfree from a Petty Nuzlocke challenge really got portrayed with a grand and enjoyable character.
Dark - Umbreon, of the eeveelutions, Umbreon's my favourite, as well as my all-round favourite dark-type.
Dragon - Flygon, They manage cool and adorable just fine. Especially their red eye-shields make their designs likeable.
Electric - Ampharos, cute...as...hell, and my favourite of gen II.
Fighting - Lucario, stumbled upon him on accident one day, loved the design so much that he preluded my comeback to the pokémon fandom after I lost it just around the start of the third gen, also my favourite of gen IV.
Fire - Cyndaquil, always picked that one as my starter for silver. They look very adorable, and their usually timid character makes that only better.
Flying - Lugia, because even legendaries can be so cute they make your head explode.
Ghost - Gengar, It's the cheeky grin it always has that gets me the most I think.
Grass - Being the kangaroo-lover I usually am, there's no way I can resist a 'rooshroom like Breloom. Breloom's also my favourite gen III pokémon, and perhaps my all-round favourite pokémon as well, but that is very much debatable.
Ground - Sandshrew, much like most of the others here. Too adorable not to mention.
Ice - Delibird, santa penguin, lovely.
Normal - Kangaskhan, no explanation necessary for this, if yes, see Breloom. Along with Slowbro, my favourite for gen I.
Poison - Croagunk, so much cooler than Toxicroak.
Psychic - Wobbufet, most hilarious character on team rocket's side, bar Meowth.
Rock - Rhydon, awesome pokémon. May not really have much with rock-types, but I still like its design.
Steel - Skarmory, Always has been a must-have for my team. Just amazing in combat, and a cool design.
Water - Slowbro, already having been mentioned, is one of my favourite pokémon from gen I.