Hi, I'm new to this site but it seemed liked a great place to get an answer about the 天使 of SPN. I am just curious: Is Gabriel a higher ranking エンジェル than Castiel?

In the bible (I’m not a bible thumper, just bringing ホーム a point) the archangels are higher in the ranks than ‘regular’ angels. Gabriel is an archangel so, yes he is a higher ranking angel.

Yup! He's an arch-Angel while Castiel is just "regular" Angel.