[Closed] Recommend me a "Home CCTV System"

There are so many out there and can't work out where is worth spending the cash. happy to pay for quality if I can then move them to the next house.
External cameras required not bothered about interal.
Not worried about being ableto use my iphone app, although would be nice.
I already have a NAS and a number of spare USB drives I could use if required.

upgradeable for another house (and more cameras) if I'm likely to take it with me. otherwise, i'll leave it as installed.

What other things should I be looking for?