i had one that was pretty stuck , on my old Dakota i used a 2ft pipe wrench after you break the seal it should come pretty easy, or like the other guys said just slip a piece of pipe on the end of a pipe wrench to get the leverage

 

If you don't care about the ball and are just gonna toss it when you take it off then go with RH's pipe wrench and breaker bar solution. Have done it many times to remove an old rusty one that was destined for the garbage can...