Asking this question is like asking for everyone's personal opinion - there is no single answer for this question.
The best guideline is in the OWNERS MANUAL or the FACTORY SERVICE MANUAL.
There is no mention that is has to be synthetic.
IMNSHO, regular mineral oil is fine.
Synths are a waste of money, unless you "need" the higher performance synthetics will afford you.
If it's a daily driver, it's a royal waste of money.
All popular name brand oils - IN NO PARTICULAR ORDER: Mobil1, Castrol, Valvoline, Pennzoil, Quaker State, Shell, Chevron - are all fine.