It is down to personal preference. Both are leading manufacturers of Hard Drives. I have 2 hard drives in my PC - one main drive and the other one I clone to. One is Seagate and the other is Western Digital. To answer your query, which is better - I personally don't find any difference, but I am sure there are others who do.
Sony Xperia Z5 review: Hands-on with the phone which the Z3+ should have been