5S naked. Phone cases are a silly waste of money.
A good quality slim bumper is the best of compromises.
Think about it. Even your aluminum MacBook has 4 small silicone feet on the bottom for scratch protection and non slippage.
A bumper gives the same for front/back and side lay on the table usage. And dropping.
Actually, those feet are to prevent the MacBook from laying flat on a surface and overheating.
5S naked. Phone cases are a silly waste of money.