Is making your base more defensive better than worrying about your offensive capabilities? And which would help your campaign more in the long run?
Defense is pretty important in Clash of Clans. If your defense was somehow impenetrable, and you were infinitely patient, you could technically acquire all the resources you need for upgrades just by waiting and tapping your collectors occasionally.
However, no defense is perfectly impenetrable. Someone who spends a lot of time or money on the game can bypass virtually any defense. They're coming, and they'll take your resources. Also, very few people are infinitely patient.
Thus, raiding is the way most people get most of their resources, so offensive capability should not be neglected.
All that said, there's no reason to neglect either of them. Most defensive buildings require gold, while most offensive buildings and units require some type of elixir. Builders can be somewhat scarce, but honestly you should be prioritizing both of them in order to get ahead.
I suggest you do both offense and defense. While you have a shield, work on defense. But when you have no shield, upgrade offense and be ready to attack 2-3+ bases. When you decide to upgrade at the opposite time,try to do 1 offense and 1 defense.