I go through white tops with such a fervor that it's simply ridiculous. Though they happen to be a critical component of my wardrobe, I refuse to wear them once they've lost that crisp look and feel. Between underarm stains (due to deodorant), a baggy fit by the end of the day, and transparency issues, it's hard to find just the right white top. That's why I've done my research and have come up with my favorite.
Though I already own an LnA shirt, this long-sleeved option is clearly a necessity. Since the brand runs big (and stretches out), be ready to buy one or two sizes smaller than normal.
TIP: In order to remove underarm stains, soak in disolved powdered aspirin (5 tablets per liter of water) for 1-2 days.