In my opinion, it's a trade off. Synthetics are going to cost a lot more, but they should make your engine last longer if you follow the manufacturers instructions to the letter. I know some people swear by AMSOIL, but I can't justify the cost on my equipment.
For my money, any name brand oil is good. I buy whatever is on sale at the auto parts store among the top brands, which are probably Pennzoil, Castrol, Havoline, and a few others. My father makes me laugh because he still swears that Castrol contains castor oil, which I doubt is true, although it may have been at one time.
I think THE most important thing is not the brand or type, it's how often you change the oil and filter. I have opened up motors with 100,000 miles on them and they look brand new inside, largely because the oil was changed regularly. Hope this helps.