What counts as metal?

[ABlairican Pie]

Are these bands metal? And which is better, "old" metal or NU-metal?

Linkin Park
Staind
Disturbed
Nickelback
Creed
Default
Limp Bizkit
Korn
Papa Roach
System of a Down
Tool
Puddle of Mudd
Rage Against the Machine
Sevendust
Slipknot