Why wont my car start up at certain times?

[kdewayne1991]

I have a 1999 Chevrolet Cavalier. The problem is is that sometimes when I start up my car it wont crank up until the 2nd or 3rd time and at other times its perfectly fine....also my gas gauge used to fly all over the place but today its been normal. I have been told that I need a new fuel pump and I have been told I need a new battery. Which one is it most likely?