I have used both the flip covers as well as back covers for my mobile phones. From my experience, I find back covers look more aesthetic, gives a slimmer look to the phone and is easier to carry in the pockets, while flipcover offers greater protection to the mobile screen, has tougher overall look and protection. It is the bulky look which it imparts. that is a real put off, plus the inability to carry the phone so easily in sports-pants pockets. Although, I am all for the aesthetic appearance, I have resorted to flip cover for better screen protection after changing 3 screens due to cracks after mobiles falling down. What is your experience and preferance?
