2005 C-6 Best Oil?

Hello, Thank you in advance for any help on this.

I recently bought an '05 C6 convertible. 6.0L, 6 Speed.

Just wondering what the best oil is to keep in it.

Mobile 1 Synthetic 5-30?

Someone told me to use 1 Quart Synthetic and the rest regular?

Any suggestions?

2005 C-6 Best Oil?