Well, a lead is the pokemon you put in front in the front of your party. It should be designed to allow you to gain control of the match from the start. A few ways to do this are with speed, with a choice scarf, with a pokemon that covers other common leads, or a baton passer...
Pokemon that I've seen lead...
Roserade
Breloom
Salamance
Gyrados
Lucario
Brozong
Tyranitar
Infernape
Forrettress
There are others, too, but I think you get the idea
Pokemon that I've seen lead...
Roserade
Breloom
Salamance
Gyrados
Lucario
Brozong
Tyranitar
Infernape
Forrettress
There are others, too, but I think you get the idea