In my eyes, it's definitely the Seagate Barracuda. I have only ever used the Barracuda in my systems and have never had any problems. It is possible that the WD Black is minimally more efficient (less than 1.5W) and a little quieter, but the price of 191% more than the Barracuda is simply not worth it. I have yet to have a drive fail.
Both have the same rpm and the same amount of cache.
For the money, you can buy a good SSD, which puts the boot times in the shade anyway, and reduces the noise, because it may be written to the SSD and not to the HDD.

So in my eyes, the Seagate Barracuda (2TB, 3.5", Desktop, Server) is for sure.

I'm not going to answer both questions the same way... Google this, you'll find lots of benchamrks and user feedback: http://hdd.userbenchmark.com/Compare... or http://www.tomshardware.co.uk/answers... If the extra price is worth it, I'd go for the Black. It also has a longer warranty and lower power consumption. The cache is the same size for both. The Black is a little faster when it comes to continuous writing/reading, hence this one ;-)