Just today as I'm replaying White I caught Zekrom after one SE Ground attack and a single Quick Ball. Would it really be valid to say "I don't know why people had to throw a ton of Ultra Balls at him"? Your experience isn't always the norm--before now I had NEVER caught a Legendary this easy, they would break out of 20 Ultra Balls while having 1% health and Paralyzed if I was lucky.
Zekky & Reshi in black/white 1 were purposely easy because you are forced to catch them to progress the story.
It's a pleasure when you treasure all that's new & true & gay! http://i.imgur.com/VBsWOu2.png <3 We are one having fun walking in the glow of love..
Whitney hands down. Her Clefairy is a joke, but dat Miltank. It's got a much higher BST than your 'mons, extreme flinchhax, and Attract, which is wholly cheap. It is very evil.
Honestly I can't say who is second most difficult 3rd Gym Leader, simply because the only Pokemon games I've played in a very long while is Black 1 and White 2.
You can actually destroy miltank easily if you take advantage of clefairy and boost your pokemons stats up. However this is not saying much. I beat Cynthia on a pearl file with a level 50 gyarados doing just that.