Anakin Skywalker: Motivation (First Draft)
Anakin is very much emotionally and morally motivated, with emotion taking priority over morality. When looking at why he does anything, it's important to know that he doesn't put any kind of rational thought into any of it. If he does, then he can only hope that he doesn't have enough time to dwell on it, because he'll inevitably act according to his heart.*
I'm not trying to say that he never could, never has, or never will act according to his brain. I'm just saying that those instances are few and far between, or he chooses with his mind and then back tracks later.
He acts according to his heart, which really is in the right place and always has been, but he's virtually incapable of logical reasoning, so his actions don't always follow his morality.
To know what Anakin will do in any given situation, all you need to know is what's important to him. We know people are more important than anything (people in general with people close to him taking higher priority), so we can always know without a doubt, that Anakin will do whatever he can to protect those he cares about. Even if that means going very far outside his moral compass.
*He initially chose good and reported Palpatine to the Jedi, but he had too much time to dwell on it, and his emotions won out.