Both oil and sugar will help maintain moisture. The oil is better at helping the dough retain moisture before baking, and the sugar is better at helping the dough retain moisture during baking, but they both share roles in both cases. What's difficult about increasing moisture by some arbitrary amount is that the crust will not be "baked" until a certain lower level of moisture remains, or something with better thermal conductivity than water (e.g. sugar, oil) supplements the baking process. This is why deep frying a food in oil turns out a browned product, versus boiling a food in water. The Maillard reaction and caramelization that's responsible for browning only happens at specific temperatures, and as long as a lot of water remains in the dough, those reactions won't happen.
For you're own personal tastes, you will have to test doughs with higher oil, sugar, or oil and sugar to see what results you like best.
EDIT: Since you mentioned also wanting a crispy outside, it's almost a no-brainer. What you want to do is oil your dough and pan before going in the oven.