If you have not done much tube changing, then I say go with a pump unless you plan on carrying at least two or more cartridges.

When I started biking, the LBS sold me a CO2 inflator because they thought it will be easy for me to get the pressure up easier than a pump. On my first flat, I used one cartridge just to find out 1/2 miles later, I still had some more goat head stucked in my tire. No choice but to patch that tire and went another 1/2 miles to find out that I pinched the tube to the tire. Out of cartridge so ended up walking bike home.

Even today, on my 700x23 tires, I still sometime get the tube caught on the bead. There's not a whole lot of room to work with and when they are tough to get on which is typical of some tires like the Armadillo, there are chances of getting a second flat. So carry much more needed CO2 cartridge than needed, otherwise go with a pump. Also with a pump you can help another cyclist in distress when they get a flat