I actually tried to do both.
I considered the standing of each patron and matched them with elements that balanced out.
The Undying (now Tormented) would be very strong and aggressive compared to the rest, so it got the weakest EB. Coincidentally, it has a powerful feature that scales with damage, which is hard to abuse with a heavily-resisted damage type. Even considering the poison, would someone pick it? I like to think so.
Archfey doesn't have much damage in its features, and so got a fairly universal element (Acid).
Similarly, Wizard schools are matched up with an inversely powerful magic type. Divination is the weakest magic type, yet has some of the most powerful features. Transmutation is the most versatile of the magic types for Wizard, yet the school provides hardly any combat benefit. As a result, all of the Wizard schools are "even". I tried to follow that practice, so that every Patron is a difficult choice to make. That way, making a choice is mostly dependent on what kind of option fits your concept, rather than one providing a strictly mechanical increment.