I am an overworked expert on this subject.
conventional is good for older, especially inline and older, let the valve seals get their burnable drips.
syntec blend is somnething most can get away with, any year.
full synthetic can go to most all aluminums..old irons hate it however, it is a long stinky road on the old irons...and it may even fail with it.
today, go for oils at manufacture date, most if not all the gassers can take anything...of course synthetic is amazing, get the right ratings for your car, and even beyond. 20 years old or so, you have to look up your cars humble demand.