While I’m not an authority on this, I’ll take a crack at answering this one. It would be a good idea to research my statements. While I believe them to be correct, I could be missing something.
To know which one is “best” for you, it helps to know some of the differences. Intel XEON vs. Core I vs. Celeron. XEON CPUs are intended for servers, but the biggest difference as far as I know is in the L2 and L3 cache. Celerons have the least, and Xeons have the most.
Clock speed: generally, the faster the speed, the more heat they generate. For a Mini ITX system, the focus is usually on power consumption. If you are trying to keep the light bill down, try not to go more than a Core i5. Also, try to stay around 2.4 to 3 GHz. The faster clock speeds can help, especially if you have multiple cameras, but they are less important when you have a decent GPU to help. The more heat you produce, the more fans you’d need, etc. It is a good idea to setup a test system for reference, so that you have an idea how much more “oomph” you need.