How do you say "You're a catch." or "She's a catch." in Korean?
In English we would use this phrase to describe someone we thought was especially valuable in the context of a romantic relationship.

Question

Answer

You could use the words as Philip said, and of course if you were to use a sentence,

you could say

"그 사람 참 괜찮아"
"그 여자 참 괜찮아"
"그 남자 참 괜찮아"
"그 사람 진짜 괜찮아"
"그 여자 진짜 괜찮아(요)"
"그 남자 진짜 괜찮아(요)"
"진짜 괜찮은 사람이에요"

"괜찮아"  here means more than fine/alright, and it is okay to use one of the sentences when talking to friends/parents/coworkers...etc.

Among girls when we talk about a guy who is deemed to be a catch, some ppl say
 "괜찮은데, 잘 키워 봐" 
of course, this is among close friends who share inside jokes/homour.

Hope this helps!

Answer

훈남 for a boy and 훈녀 for a girl.

It means a really pretty and handsome person that makes you feel warm inside because of her or his greatness :)