Auras..

Maybe this will help you decide which one you think is the best deal for you.

http://www.youtube.com/watch?v=tI26OWPOqWs

T4 Aura Rates (projected):
Fishing:

C2 - 111,628: unaffected
Barbarian - 117,632/99,088: 18% increase
Rocktail - 105,080/50,360: 108% increase

Woodcutting:

Ivy - 122,940/81,960: 50% increase
Sawmill - 111,240: unaffected
Arctic Pine - 157,248/131,040: 20% increase

Hunter:

Draconics - 346,500/288,750: 20% increase
Zamoraks - 264,000/198,000: 33% increase
Black Warlocks - varies highly ~219k MAX: unaffected

Thieving:

Pyramid Plunder - 334,000/300,600: 11% increase
Dwarf Traders 343,375/220,806: 56% increase
Monkey Knife Fighters - 288,000: essentially unaffected

Mining

Concentrated Gold - 110,085/95,600: 15% increase