The ideal motivator for work is to be in a situation in which we are able to give and keep on giving. We give our time; attention; compassion; or whatever else we have in so much abundance of, that the only thing to do with it is to give it away. It also helps that we strongly believe that what we have to give is what others lack but really have to have, no exceptions.
Everyone has the ability to tap into this abundance, each in their own way. To identify what we have that there is overflowing abundance of, just look for what we love most to do. It's the one thing we want to do to the exclusion of every other activity. That which we do or exercise most often is the thing we become best at. We would even continue to do that even if we weren't paid for it. Thing is, when we work hard at something enough to get really good at it, people will pay us just because we are that good.
Being employed, however, is a 'take' scenario. We do our job because we want to take our salary. Employers take our time and effort, and anything else they can squeeze from us because they damn well can because they paid for it. In a 'take' situation, everyone in the relationship runs dry pretty quickly because they are taking what no one is prepared to give without getting something back in return. As such, everybody gives only the minimum effort possible commensurate with the minimal wage one is given.
Because we put down our tools as quickly as we possibly can and go find something else we would rather be doing (which is clearly not the thing we are being paid to do), no one stretches, grows, develops or becomes good at their job. We hit a plateau, our career stalls and our employer starts to consider other options that may prove more value for money -- a machine, perhaps; or a hungry, young foreigner willing to give a little more.
So the best job to have is the one in which we are prepared to give without expectation of return. Not of the money sort, anyway. The return we should expect to get is the learning through daily experience, making us better at our jobs than we were the day before. I'm not saying that slaves have the best job in the world because for them it is all take and no give. I'm saying that if we can see ourselves doing it better and better every day, this is the job we were meant to do, salary notwithstanding.
... I've always dreamed of driving a delivery truck across country. I think I could get real good at that.