Simple: Mercon V is all you need for your 2008's transmission (and power steering). You can go aftermarket brands with good success, stick to Castrol Transmax, Valvoline, Royal Purple, Amsoil, even store brands that have received good reviews.
DO NOT use Mercon LV, that's for use on later model years and is NOT compatible with your 2008.
The PTU and RDU use gear oil, not transmission fluid.