Well, there are a few common leads in LC, and some less common. They usually serve one of 4 purposes: set up SR, set up weather, fake out lead(or pivot lead, ie purpose is to damage+ gain momentum in your favor) or be an anti-lead that counters one/multiple of the former. SR users are usually stuff like gligar/diglett/bronzor, less common stuff like phanphy and chimchar, fake out is stuff like meowth, less common is glameow, weather users are snover/hippopotas/aipom (sunny day) / voltorb (RD), anti leades are stuff like machop, houndour, etc.
most of those are common leads you would see in LC, and I'd say if you're going HO carvanha, if you're going more bulky, buizel.
hope that helps :)