I'm presuming it's sequential data, then if so then purple.
Golds (now renamed ultrastars) are more suited to random IO such as database operations with high queue requests, dam good drives however I use gold's on my software dev workstation, In the history of HDD's WD Golds are probably the best sata HDD's drives ever made.
For best reliability all HDD's should have some gentle cooling (air) passing over them.