One thing to consider is all major brand oil is certified. They are similar as far as meeting the certification requirement. If you change your oil regularly, it really doesn't make a difference which brand you choose. As fro the weight ex. 10w40,5w30) . You will want to use the manufacturer recommended oil weight. The weight of the oil is the last number. The First number is related to what temperature it is good for. So if it is colder out you will want to use 5w30 and in warmer climate, the 10w30 is better.
Synthetic oil is superior to conventional oil. Synthetic oil lasts longer before it starts to break down. Synthetic oil also leaves a thin coating on the cylinder walls to help prevent damage at initial start up.