Which jungles have the fastest clear speeds?

Virtually anyone with an AOE ability, and the ability to face tank Raptors before level 4.

Like Volibear, Shyvanna, Amumu, etc.

can reach level 3 with almost full hp ( starting blue) ,

top1 base attack speed, top1 base ad, sapling insane %hp damage from bush IN AOE

try him and you will see

In terms of the first clear, Mundo is the absolute fastest, provided you use AS runes and start E like you should.