The Efron family's got some good genes ... 'cause Zac and Dylan Efron are a set of seriously hunky brothers!

Zac's been a heartthrob for years ... but his younger sibling has recently found himself in the spotlight thanks to his well-received participation -- and big win -- on the reality competition show "The Traitors."

It seems like fans have plenty of room in their hearts for both Efron brothers ... but who will rank supreme on the beefcake meter? The famous siblings enjoyed a boat day recently ... and looked quite fine as they soaked up the sun. But the question here is: Who'd You Rather?!