When used with the word vara (VA-da, lit. thin stick) in aguantar vara, it is a reference to the days of irresponsible parenting and repressive education, when infants were spanked with sticks. Aguantar vara means to endure or tough out a difficult or painful situation (just like little children used to endure the spanking before psychologists figured out its long term consequences and banned it).
When someone is discussing certain attributes, aguantar un piano (lit. to support a piano)—or any other heavy object—means to excel in terms of those attributes. When it is used without any context to refer to people, it almost surely is a positive allusion to physical beauty.
Después de aguantar vara más tres años, finalmente renuncié => After more than three years of puting up with their shizzle I finally quit my job
Las vecinas del depa de arriba aguantan un piano (cada una) => The neighbors in the flat upstairs are really hot (all of them)
Aguántame una semana y te pago todo lo que te debo => Give me one week and I’ll pay back all I owe you
Aguantar vara can be seen as a sign of endurance or stupidity