As long as they do not already leak and do not have issues, running synthetic of any kind is best. The number one thing to consider when choosing which oil to run is how you want to maintain your vehicle and your budget. Paying close attention to the recommended drain/change intervals from the manufacturer of the oil you are considering, stick to their recommended intervals or less. Some companies offer longer service intervals than others. Those that offer the longest service intervals will save folks more money over time if they change their oil according to the recommended intervals.
For example, Amsoil Signature Series 5w-30 has a service interval of 25K miles or one year whichever comes first. Most people don't drive that much, the national average is around 13-15K per year so you would be changing your oil once a year.
No matter what you choose to use, make sure to stick to the recommend intervals or less and you will be just fine.