I'd recommend Blue Iris if you have a PC that can handle it and don't mind it running 24/7. I monitor 23 cameras using BI and am continually amazed at the many configuration options of the software. I know others will recommend NVR's but I will always prefer BI.
It really depends on your needs and budget. Blue iris is much more flexible than any NVR out there however will require a powerful pc to run it. You could not pay me to use a standalone NVR unless its a backup recording 24/7.
Has anyone here run BI on a VM? I might buy a simple Lenovo server and run BI on a Windows VM as well as run other VMs for things such as Plex, fileserver, etc.