I think most fans have a unevolved Pokémon that they really like, sometimes even more than their evolved form. For me, I like Snivy, Magby, Mareanie, Popplio, and Mime. Jr more than their evolutions. The reasonings being... Snivy - Was what got me back into Pokémon, so it is very special to me. I guess I wanted it to evolve into something really special, but Serperior didn't do that for me to be honest. I mean, I don't hate it, I just find it disappointing and not very interesting design-wise. Servine is alright though, but still not as great as Snivy. Magby - Don't get me wrong I love Magmar and Magmortar, but Magby will always be my favourite due to its cute design. It's also one of my top 5 favourite Johto mons. Mareanie - Once again, I don't hate Toxapex at all, I just prefer Mareanie's design a bit more. I think it is super cute, but at the same time not that 'generic' sort of cute, which I appreciate. Popplio - I like Brionne and Primarina. Hell, Brionne is probably my favourite middle stage starter, but Popplio still remains to be my favourite in the line. I really love it's cute design, which was the reason I was on team Popplio when it was first revealed (until Incineroar was leaked, of course). Mime. Jr - It's probably kind of obvious as to why I prefer this adorable mon over its creepy, ugly evolution. Such shame it evolves into Mr. Mime...
Personally, I like Vigoroth more than Slaking. Even though Slaking is easily one of the strongest Pokémon in the game, its design and ability make it less appealing to me.
If i were to make a list I would have to put Vanillite on top. It's so adorable as a cute little ice cream. Also, Dewott. I hate almost everything about Samaurott, at least design wise. Thinking about it, most Pokémon have less attractive designs when they reach their final form, at least in my mind.
Dragonair was the first one to come to mind. I don't dislike Dragonite, I just prever Dratini and Dragonair over it. While I don't hate Trevenant, I don't really like it, either. I very much prefer Phantump.
Tepig, Grovyle, Mime Jr, Smoochum, Elektabuzz, Paras, Bulbasaur, Piplup, Braixen, Psyduck, Goldeen, Wooper, Fletchinder, Chespin, Oshawott, Popplio, Haunter, Bronzor, Gothita, Crabrawler, Jigglypuff, Quilava, Bonsly, Mantyke, Zigzagoon, Nuzleaf, Lombre, Wingull, Spoink, Spheal, Buizel, Croagunk, Herdier, Pansear, Panpour, Munna, Scraggy, Bunnelby, Litleo, Espurr, Spritzee, and Poipole.
Joltik It's just so smol and cute! It's perfect the way it is! ;w; Drifloon I think it has a nice iconic look that it's evolved form loses a little. Chikorita I don't dislike the evolved forms of Chikorita but I do prefer it as a smol. Fennekin and Braixen I'm just not a huge fan of delphox Litten I just like my cat Pokémon to remain on all fours ;A; Also it's really cute and grumpy looking. Like my cat. Chespin Another cutie that I feel just gets less cute as it evolves. ;w; Another vote for Dragonair It's just so elegant. And dragonite is just not elegant. Cute, but not elegant. Bonus mention of Zygarde even if it's just a form change? I love the Core form so much. ;w; So cute.
Joltik for sure. And another vote for the elegant Dragonair. I still can't really get over how derp Dragonite is over its pre-evolutions. Also Dewott. I love it more than Samurott.
Quite obviously, Eevee. It's just SOOO CUTE and it seems like its evolutions fail to live up to expectations. Oshawott and Chespin also on the list, Chesnaught looks weird IMO and while Samurott looks cool, Oshawott is just cute.
I don't think there's any Pokémon I'd go out of my way not to evolve because I liked it better unevolved, although I do sometimes keep an Eevee just as an Eevee, because I think keeping it a normal type is just as viable as making it evolve into another type. Usually if there's a Pokémon I'm not a fan of, it's a middle evolution so I just let it evolve and then evolve again. I tend to use a Chansey with an Eviolite too, but between the two I do actually prefer Blissey.
You know, mega evolution is a problem to me. I mean, there was some time that Pokémon was like: YEAH, HAVE THIS USELESS BABY! IT IS WEAKER AND HARD TO GET and even worse to evolve! And then sometimes we would have an evolution or something... Mega evolutions solve that but not really... which is unfortunate. So yeah, I would like Torkoal to have an evolution... I like him, but it nevers get past Camerupt if I didn't catch a Blaziken. I would adore for all the pikachu clones to have evolutions. Delibird definitely deserves one. As for mega evolution, who really, REALLY could use one is Castform. Something that locks them in one form but make their passive change to something based on said weather.
Usually for me, I like the evolution better than the pre-evolved Pokémon and there are few exceptions. One such exception is Nidorino. Back when I played gold, I had a Nidorino and I wanted it to evolve so I grided it to be the highest level party member at all times. I slowly grew to love the form of Nidorino and when I found a moon stone, I chose not to evolve it. I like Nidorino that much. It still remains one of the only times I haven't evolved a Pokémon on my party.
This, is not unocmmon for me to keep it unevolve when I use one actually, even if is rare for me to use that line. Also Bunnelby, I'm not a fan of Digerby's design even if I've used one in runs before it just don't really appeal to me.
Dragonair definitely comes to mind. I also think Mime Jr. has a better design than Mr. Mime. I prefer Roselia over Roserade design wise... also Frillish over Jellicent, Elgyem over Beheeyem, Litwick over Lampent, Braixen over Delphox, Espurr over Meowstic, Inkay over Malamar, Amaura over Aurorus, and Poipole over Naganadel.
Personally, I prefer Frillish over Jellicent. Idk, those evolved forms seem so... lumpy. And then there's of course that purple UB thing whose evolution looks ugly AF to me. Spheal over Walrein for spherical reasons. Cutefly over Rebombee... The list goes on and on and on.
fennekin,froakie,ivysaur,Skiddo,etc quite a big list actually ._. guess I have a thing for unevolved Pokémon
I have a soft spot for Nidorino, as it was the very first Pokémon I was ever introduced to (I got a keychain of it as a present from my cousin!) That said, I still really like Nidoking, but Nidorino will always hold special place in my heart. Oh, one Pokémon I think is absolutely better than both of its evolutions is Hoppip. It's just adorable. Why couldn't it keep its goofy little helicopter leafs as it grew up?
I can't believe I forgot Dragonair! Seriously, it's one of my top 10 favourite dragon types, but I absolutely cannot stand Dragonite. It's one of my most disliked Pokémon ever because I think it ruined the line. Poor Dragonair. It deserved better... Another Pokémon I really like but can't stand it's evolution is Cutiefly. I really love the way it was designed, but Ribombee? No way. I still don't understand why game Freak decided to turn Cutiefly, a mon with a really adorable but unique design, into... whatever Ribombee is. Ugh. It's a shame really, because I'd actually love Ribombee if they had kept it face the same as Cutiefly's. It's the generic cutesy face that ruins it for me...
Alolan Vulpix Bulbasaur Cyndaquil Quilava Chespin Fennekin Larvitar Skitty Shinx ... I could go on and on but I'm stopping here.