For the same price? Castrol of course. The only reason to buy store brand mystery maker products is to save some money. If there is no savings, don't even think about it.
BTW, Castrol has been owned by BP for many years now.
Castrol for sure! Contracted operations (i.e. Supertech made by some poor soul on a low margin and getting beaten mercilessly by Wallyworld) and quality assurance are not always complimentary concepts. This decision is REAL easy when both are the same price.