I have used the connectors and they are a huge pain in the butt to do. Getting the grids tight in them involves pliers to hold it in place while you hammer the connector on. Doing this for the dozens of connectors needed for a cage and it gets annoying. I also find that they don't always line up right. Also, if you want to change anything or need to fix something, you need to take off the connectors then try to get them back on again. Due to the spacing that the connectors add, you do need to make sure you take it into account when measuring for the coroplast (or whatever you use for the bottom).
Zip ties are much easier for me. It can take a bit longer to get the structure to the point where it an stand up easier and it is a bit harder to add to the height if the cage is already built. Zip ties also make it easy to make a pen as you can just fold it up when you are done.
I have a cage that is 2X3X4 made with the connectors and one that is 2X4X5 that is made with the zip ties. I don't find one to be any sturdier than the other.
If you do use the connectors, you should still use some zip ties to make sure it is safe.