Which is a more biblical boy name?
They’re equally biblical in the sense that they’re both in the bible. Seth is of course a less common name, and also the Seth in the bible is not a very detailed or important player- he was a son of Adam and Eve, God’s replacement for Abel after Cain killed Abel. Jacob of course is the biblical patriarch, son of Isaac. He was not an entirely nice person, tricking his brother Esau out of his birthright and blessing on two separate occasions, although he’s ultimately an important figure in Judeo-Christian history. It’s also a very, very popular name, so people may not immediately recognize it as “biblical” as opposed to just “popular”. Hope that helps.
They are both bible names, so I don’t see how one can be more biblical than the other. As far as popularity is concerned, more page time is devoted to the life of Jacob over Seth, so Jacob would be the better known name. I personally like the name Seth, but if you want a name with nickname options Jacob can be shortened to Jake.