Oil. Stick with a brand-name non-sythetic oil. I don't like Quaker State or Pennzoil, but pretty much any other brand name is a good oil. Castrol and Valvoline are my two first choices.
There is nothing wrong with synthetic but people choose it for the wrong reasons. If you want an extra 5-30% oil life, do it, but synthetic doesn't lubricate any differntly. Its a purer oil, but its the same molecule. The purer oil is able to dissolve more additives as well as more contaminants from combustion. The problem is that it may extend your oil life by as little as 5% or as much as 200%. The only way to know is to have the oil tested frequently. I've used synthetic before, but I truly think if you have two identical engines and use synth in one and dino in the other, they will both last the same amount of time provided you change the oil on schedule.