You are doing the same as us, we kept looking at all the options, but then finding something that put a spanner in the works for each system, in the end, we said sod it, and decided to pay a little more and get the one that ticked all the boxes.
You need to make a list of features you need, want, would like, and definitely don't want, as you look at each system, and don't forget a lot of the ones on Ebay tell fibs about how good they are!! Then compare each system to it, before deciding on what features you can bend to suit your specific application.
Like I have already said, for me, BNC coax systems are a royal pain in the butt. It's lossy, easy to damage, and hard to work with. You can take a system out with just a pin through the coax, which is easy to do, but hard to find...
Viewing angle is important, we wanted ours basically in each corner, so around 90degrees was about right, the wider the angle, the less usable distance, and the more chance of getting glare back from nearby objects.
With Cat5, you can spend a little more, and do like I did with a separate PoE hub, which means you can actually run fewer cables back to the NVR, making it easier to hide.
