People find squirtle annoying because they hate how a pokemon with an immature personality could beat other pokemon so easily. However, I don't understand why squirtle gets so much hatred, as cute unevolved pokemon have acted surprisingly powerful for quite a while. I've heard that squirtle's learning ice beam randomly bugged some people. I don't see why that would get on people's nerves though.
Also, people think that bulbasaur and squirtle make May's team too much like Ash's especially since she has beautifly, which could be interpreted as her answer to Ash's butterfree. I agree that bulbasaur and squirtle is a little too much of history repeating itself, as the game titles were fire red and leaf green, so she should have gotten charizard. Yes, I know that she already had a fire pokemon, but I still think it's unfair for both the pokemon to get more screentime while charmander evolved so quickly, and got so much less screentime with nothing to make up for it.
As for eevee, I have no idea. I guess there are some people who just hate cute. One must remember that people who watch a show about creatures who fight want to see big powerful creatures, no matter how little sense it makes.
*prepares for a fierce smashing*