I don't agree with Gyaradaos and Dragonite, I find them very easy to deal with in the gyms, due to their double weaknesses. They are usually my fastest victories. Even a relatively low cp pokemon of the right elemental type (lightning for Gyrados, ice for Dragonite) can deal with them in most instances. If you use a same or higher cp mon then it is a no contest. Double weakness is super exploitable.
I agree with the others, though. Especially remove golden berry feeding Blissey. Argh. Even with lvl 30+ fighting set machamps it is annoying to deal with. I gave up when I found the Blissey back at full hp after 2-3 KOs in most instances. And, unlike Chansey, Blissey can put some good damage on fighting pokemons with super effective attacks if you miss your dodge. A total waste of time, battery and potions. Frustrating.
I don't know how the new cp update nerfed Blissey, though. Is it now less annoying to deal with?