Motor oil is one of those things that's full of brands, boasts and BS. It's actually really easy to get the right motor oil and move on with your life. Here's a synopsis of what you need to know to select the right oil for your car. See the video for the full story and a look behind all those numbers.
(By the way if you're looking for a religious discussion of synthetic vs. conventional, you came to the wrong church. There's ample bloviation on that topic online.)
This is easy: There's oil for diesel engines and oil for gas engines. Use the kind made for the engine you have. It will be stated clearly on the bottle, or you can look for the S for gas and C for diesel on the round grade label, which we explain in a moment.
This is the oil's viscosity, expressed as a number like 5W-20. The 5 in this example is the cold viscosity and 20 is the hot viscosity at the engine's full running temp. Use what your car's owner's manual says; Nobody knows the needs of your car's engine like the company that made it. No, not even your shadetree mechanic cousin who has a lot of really awesome tools.
Engine oil weights have been getting increasingly lighter over the years as that serves both tighter engine tolerances and MPG targets best. Oildepot indicates the best selling motor oil weights are 5W-30 and 5W-20, with the even lighter 0W-20 catching up.
This largely determines the additive package that has been added to the oil and is reflected in the top of the "donut" label we saw above. But this isn't like real donuts where you would like clean and pure: You want it rich with additives that your car's engine expects to be bathed in.
The two main grades sold today are SN and SP. As the alphabet code suggests, SP supercedes SN so you can use it if your car calls for SN or SP. But if your car calls for SP, use that, but not the older SN.
Now get the real story on how often you should change your oil.