Nows the time since this wardrobe staple never goes out of style.... But it's on SALE right now. 

What to look for: 

High waist (part trendy, part "if you're gonna wear short shorts cover something else up")
Flattering whiskering, like contour, but for your butt and thighs 
Fit Fit Fit (don't be afraid to buy and return)
If you want vintage: 
Try but go by the flat measurement, not the size! size fluctuates so much throughout the years! For example, these are a men's 34 on the label but laid flat they measure 15 inches (double that and you get my waist size which is 30) probably the result of some shrinkage and also who knows or understands how sizing works?!? Not me