That is crazy. In Florida where it is warm you would want to use
10w30. Man it is in the owners manual. Read it. As for the syn. whatever floats your boat.Supposedly you can go longer between oil changes with them , but I will stick with my regular dino oil.
Other than that use whichever you feel comfortable with.
Brand doesn't matter as long as you use the weight the manual calls for.
Been using my dino oil for 30 years no problems. In short use what you want, you can't go wrong......except reconditioned oil...lol....then you are on your own.