Whenever you are buying a scrub top, first check whether it is unisex or sized for men and women separately. The scrubs sized for women feature a slight curve at the waist whereas the unisex and male scrubs feature a straight fit.
The second thing you should consider while buying a scrub top is its length. It is suggested that the length should cover you below the hips so that you can work comfortably without pulling your top down each time you bend.
For both men and women, scrub tops should not be too low cut to avoid any kind of embarassing situation when you lean on your patients to diagnose them.
Vents or side slits can help in increasing comfort and providing air.