Well For each of the gens I play there is atleast one or more of those Gym Leader types!
Gen 1: that there Misty! with her over powered Starmie!
Gen 2: has 2 ( ironic I know huh?) The first being Milta---I mean Witney and that god damn dream eater rape Gengar of Morty!
Gen 3: has Watson if you chose Treecko also Flannery`s Torkoal! , but don`t get me started with those TWINS!
Gen 4: mmmmm Gen 4 is a though one as that is the gen I come back to the least but if I have to chose it would be Crasher Wake and his Gyarados if you don't have a Electric type to use!
Gen 5: is Definitely Elesa and CLAY! Elesa because of that Emolga! and CLAY because of -Say it with me!- EXCADRILL! freakin overpowered mole!
Gen 6: uuuum Until Today I never had any trouble with any gym Leader but if Elite four count than I had trouble with Wikstrom
soo Yeah that's all!