The practical difference between an analogue and an IP CCTV system is not image quality on its own - it is the wiring, and what the system can do once it is in.
An analogue system runs coax cable from each camera back to a DVR, which does the recording and the thinking. An IP system runs Ethernet - usually Power over Ethernet, so one cable carries both power and the video feed - to a network video recorder, and each camera gets its own address on the network rather than sharing a dumb cable run. That one-cable-does-both detail is the practical win most sites notice first: no separate power run to every camera position, and a camera can go wherever the network reaches.
Hikvision and Hanwha make up most of what actually ships in IP cameras from us, with Axis and Dahua also well represented. The resolution gap between analogue and IP has mostly closed - IP's real advantage now is onboard analytics. Motion zones, line-crossing alerts and vehicle/person detection run inside the camera or the NVR on an IP system in a way a DVR-based analogue setup generally cannot match without a full recorder replacement.
Most upgrades are not a rip-and-replace. The common pattern is adding an NVR alongside new PoE cameras at the positions that need replacing or where analytics matter most, while leaving working analogue cameras and their existing coax runs in place until they are due for replacement anyway. A hybrid recorder that accepts both signal types makes that staged approach possible without throwing out cabling that still works.
If you are planning a CCTV upgrade, tell us what is already installed and what is actually not working about it - image quality, coverage gaps, or the lack of analytics - before we talk about which cameras to buy. The answer changes what the upgrade should actually include.