How much do you value speed over capacity? Or do you need both? If speed is ultimately what you need then go for an SSD. Expensive, but it will solve the problem with your millions of files and photos. If on the other hand you are after capacity, you should go for a 7200RPM drive with lots of cache. WD or Seagate does not really matter. If you need more specific models let us know, as well as what exactly you are looking for.