Which is better? I'll point out the drawbacks of both.

More Fuel
- more weight, which means slower acceleration and less efficiency (on fuel, brakes, tires, etc.)

Less Fuel
- Fuel pump works harder (I think).
- More contaminants enter the system.
- The thing about free air volume (less is said to better).

Having said that, perhaps the best thing to do is to keep the tank between 3/4 and 1/4 full. Any other insights are welcome.