As a small team's CTO doing both product management and engineering, I'd say product management is the more difficult role. Might be because I'm not as experienced, but despite having a natural aptitude for it and even after having gone through training and spent a lot of time doing it, I find the job damn hard. You're the broker for a lot of unstructured information and have to fend off all kinds of disruptive influences to land even close to where you're trying to go. I have immense respect for product leaders at innovative organizations.