Those are some good prices on HDDs. I'd personally go for the 3TB since it's $3 cheaper than buying two 1.5TB drives. Saves on USB space and has a faster USB speed out of the box.
The only problem is they're Seagate drives, and not the amazingly wonderful WD drives you can drop off a bookshelf without losing data. The last Seagate I bought was an internal Barracuda for the family PC, and some nude pics of an ex somehow became locked on the drive. You could still view the previews, but it's like the drive lost the physical location of where they were stored and you couldn't delete them...try explaining homemade softcore to your parents at 16.