Things to consider are how often you will change you oil, how often you will change your oil filter and how much do you plan to spend on maintenance based on the number of miles on the vehicle. There are 3 basic types of oil mineral based, synthetic and blended. All have pros and cons. The most important aspect is keeping oil clean and free of contaminants by changing the oil and filter (WIX or NAPA PRO pretty much set the standard for filters) often especially if you boondock on dirt roads. Mineral based oils tend to be cheaper and because they are not as slick I use them to break in rebuilt engines so wear patterns develop and create better sealing surfaces more quickly. On older design engines I use an additive to protect camshafts and followers as well. As it is cheaper I can change it at 500 miles and 3,000 mile intervals until it is broken in at around 15,500 miles. From that point on I change it every 5,000 miles and never let it go over 5,500 miles or over 6 months in the crankcase regardless of the miles. Depending on your pocket book at that point I use Valvoline Blended Synthetic as it provides most of both types of oils advantages for general purpose use at the lowest cost at the time I started using it (I don't like changing oil brands because to me wear patterns are important in my opinion and change can affect wear patterns). On older engines with over 75,000 miles I use the High Mileage version of the Valvoline Blended oil. On newer engines that the factory recommends Synthetic I use their manuals recommendations and factory filters. If the previous owner has used a particular oil, done regular maintenance and it has worked well for them for over 75,000 miles I would continue to use it and WIX filters. Once an engine is broken in with no oil leaks or residue and the manufacturer's manual allows the use of synthetic oils, if you are willing to spend the extra money required to change the oil every 5,000 miles you will see some minor benefits by using full synthetic oil. In my opinion oil changed more often provides more benefit than better oil changed less often. Toyota uses full synthetic and recommended in their 2013 4 cylinder the oil and filter be changed every 5,000 miles while in the 6 cylinder 7,500 miles. This tells me they feel extreme use warrants changes at 5,000 miles. My recommendation is if unknown what was used and the mileage is over 75,000 miles to use Valvoline High Mileage Blended Synthetic and WIX filters changed every 5,000 miles as in my opinion you can't do any better than that.
