I would go for the 7200rpm 3TB Hitachi - I have two and they are really nice drives. Shame they are in such short supply at the moment as I would like another. I think the Seagates are quite quick but I have a phobia about Seagate drives...
Sure it's the 7200rpm version (7K3000) not the 5400rpm (5K3000)? Fairly unusual to see a 7200rpm drive in an external.