There are a few varieties of Western Digital (WD) drives:
WD Black are the high performance drives. You would only use these if it is your boot drive, running programs from the drive or other activities that need high disk performance.
WD Blue are the budget drives. No benefit to be said for them except the price.
WD Green are the energy efficient bulk storage drives, designed to run cool and quiet.
WD Red are designed for NAS use (usually with RAID).
Of those, unless you are using it as your boot drive, I would choose WD Green.
The Seagate barracuda drives are very good too.
Also, you don't necessarily need SATA 3 (6 Gbps). You could easily use a SATA 2 (3 Gbps) and the drive would never saturate the link. The SATA 3 drives aren't...