Pokémon that you don't evolve into final stage

There is only one Pokemon that I never evolve.

That Pokemon is the only one that actually gets weaker upon evolution.

The Pokemon, in question, is Magikarp.

Ok, in all seriousness, I have to go with Vigoroth. At least in maingame, where I find no use for Skill Swap. Metagame, I can see it happening.

I never evolve my Mudkips or Quilava I don't know why.

I never evolve Totodile or Pikachu. Actually, there's alot of pokemon I don't evolve, primarily because I don't like the evolved forms design. Never gave a crap about stats.

I got a Pikachu that I don't evolve. Because I use it on wi-fi battles to prove that Pikachu is an awesome Pokemon despite what Pikachu haters say :)

There aren't any that I never evolve, but there are a few of which I catch more than one, so that I can evolve one and keep the other unevolved - Dragonair/Dragonite, Vigoroth/Slaking, Scyther/Scizor...

Chansey, Magneton and Vigoroth. They can all tank hits better with an Eviolite, but also, Chansey looks cuter, Magneton is faster and Vigoroth has a better ability than their pre-evolutions.

I usually evolve every Pokemon, only exception was a Vigoroth i had in Sapphire (because of his ability) and if a Pokemon can learn a certain attack his Evolution can't or needs a TM to, like Growlithe and Flamethrower. Oh yeah, and i delay stone evolutions as much as possible

I tend to avoid evolving Haunter, Graveller, Kadabra, Pidgeotto, Tranquill or Ducklett. I prefer their designs to those of their evolutions and I don't engage in competitive battling, so it doesn't really hurt my play.

I sometimes just give up and let them evolve when I get sick of hitting "B", though.

I have never had a reason to hold a pokémon back from evolution. If I want to use unevolved pokémon I'll stick with mystery dungeon.

I don't evolve Pikachu or Vigoroth. Sometimes I keep my Bulbasaur a Bulbasaur because I love them so much.

I once ran through crystal with a chikorita I didn't level. I stopped it's evolution myself until elm gave me the everstone, then I never took it off. I don't really even remember why did this, I really liked chikorita compared to it's evolutions back then. If there's any I wouldnt evolve because of design it's be gabite. I prefer it over garchomp. Another pokemon I didn't evolve once was trapinch, and I did that mostly so I could skip over vibrava heheh...