Nobility

Below royalty, but above commoners and most of the governmental class.
Whirlpool nobility is rather famous for accumulation of bloodlines. Heirs often travel to faraway lands in hopes of finding interesting individuals to marry. General racial traits such as Cotd longevity, wastelander resilience, and northen soul flow are valuable, but the real prize is in quirks- Thinker's Blessing, Su's Pact etc., especially those with binary activation state (not diminishing over time- either present or not).
The Silverthorn Pact (a heritable trait which draws from a pool of energy divided between all other living holders of said trait) became quite a point of contention in the later years, where the overwhelming majority of its pool was held by Whirlpool nobility; lots of arranged murders to thin out the herd and maximize one's own familial strength. Eventually, they went too far in their cullings, and ended up driving the entire quirk extinct within the lands.
Elemental Affinity isn't as highly regarded due to its volatility. If anything, families focus on a single elemental affinity, since mixing them always results in male children, preventing further accumulation. They often go by matrilineal dynasties: once broken, the affinity is lost, and the effort wasted. This is far riskier than accumulating small quirks which, while recessive, tend to be more highly embedded into the lineage.
The ultimate goal is supposedly to create an heir worthy of marrying into royalty. Lots of corollary benefits, of course.
As a result of this, Whirlpool nobility has a reputation for offering great freedom in marriage- really, they're just elitist in different ways. It comes down to the fact that very few political alliances are worth sacrificing a chance of ascending to royalty, and the only way to do that is to accumulate powerful bloodline traits.
That being said, it's generally possible to trace almost any commoner's ancestry back a dozen generations to find some sort of powerful lineage. The chance of these suddenly resurfacing is rare, but is often used to justify marriages for love which really can't confer any beneficial traits.