I dont think its a simple one or the other answer for which is better, a mix is ideal, but if you were to prioritize one over the other id definitely have to say hands on. Theory is useless without hands on.
Example, you could spend weeks reading about the theory behind wiring manuals and diagrams but still not imagine the real life equivalent. You might be able to pass an exam which is nice, but do one solid wiring job on an aircraft, or spend a solid day trying to troubleshoot a system using diagrams and checking connectors , checking continuity, replacing boxes or switches, and you'll know a lot lot more.