I would argue sensor size is what's most impotant to look for in a camera.

Have a look at this thread [1] I have bookmarked. I found it quite informative. I already got some cheap cameras and set them up, but I wish I would have found it earlier. The ones I got are 4MP with 1/3" sensor and perform absolutely terribly in night setting.

[1] https://ipcamtalk.com/threads/getting-cameras-with-the-right...