I use CLI for updating with sudo eopkg up. I like to have the verbose output and be able to easily cancel the update process in case of a dropped connection (during the download part of the update process) and restart the update.
For me Software Center serves more as a catalogue. I use it to search for software, check what kind of updates are available (I'm on the unstable repo so they come in often) and check the changelog. I also use it If I want to install a single item from the repo.
If I want to install multiple items, I first check the Software Center for the packages, and then I use CLI to install multiple packages at once. This mostly happens when I want to install some software from outside the repo and I need to check whether the build / runtime dependencies are available in the repo.
