FWIW I use Pennzoil Ultra class synthetic because of its detergents. Price is about $25 per 5 qt jug at Wal-Mart, so less than Seafoam but maybe on par with Rotella. They appear to be more than just marketing smoke; from their website and the bottle itself:

Pennzoil Ultra™ 0W-40 is the only motor oil trusted to be factory fill in every Chrysler® SRT8® HEMI® engine, and the new 2013 SRT® Viper®. And it's the exact same oil that Team Penske uses right-out-of-the-bottle in the IZOD IndyCar Series.

[Pennzoil Ultra Euro is] the only motor oil exclusively recommended by Ferrari North America.