Jewelers can thank athleisure wear for the growing interest in the humble hoop earring. Yet the styles they’re turning out are anything but simple: gem-studded circles, geometric and fancy-shape designs, and airy, ornate metalwork options. But trying to decide which one to wear? That could throw anyone for a loop.   (Above) Floating Tahitian pearl hoop earrings in hammered 18k yellow gold; $3,265; Jordan Alexander, Mountain Brook, Ala.; 205-868-1391; jordanalexanderjewelry.com    (Inset) Legacy hoops in oxidized sterling silver with 14k gold posts and 22 cts. t.w. moonstones; $698; Nina Nguyen Designs, Lafayette, Colo.; 720-459-7664; nina-nguyen.com   Otto diamond earrings in 18k yellow gold; $3,700; Sorellina, Brooklyn, N.Y.; meaghan@forfuturereference.com; sorellinanewyork.com   Laila hoop earrings in 18k white gold with 2.5