I personally prefer batteries, for a few reasons. First, if your battery dies out, you can always change it with a spare battery in your pocket. You are stuck with the internal rechargeable battery when it runs out. AA or AAA batteries are avaliable anywhere. Second, a normal internal rechargeable battery dies out in 1-2 years.
I WOULD LIKE TO KNOW WHICH WOULD BE BETTER IF YOU ARE BUYING AN MP3 PLAYER. AN MP3 PLAYER THAT TAKES BATTERIES OR AN MP3 PLAYER THAT IS RECHARGEABLE? AND IF YOU SAY RECHARGEABLE OR BATTERY OPERATED MP3 PLAYERS WHICH ONE WOULD YOU RECOMMEND?