pump. WTF would you carry BOTH? that's just doubling your weight penalty. A pump can inflate any number of tires, any number of times. Plus, you can use it to make funny noises against your armpit at rest stops, or beat dogs with, or stick in the wheelsucker's front wheel a la Team Cinzano.

anyway, CO2's for pusssies: if you can't use a hand pump to inflate your tires, maybe you'd better stick to knitting.