I second what Janet and Feline said - the more pressure you have to put on the needle the more you bend it. In the beginning of my "quilting career" ;-) I often used John James Betweens #12 or Richard Hemmings #12 and after a short time of using they were bent and out of shape although my quilt wasn't very tight in the hoop. I tried the #11 of JJ and it was much better.
I also found out that sharp needles are not as sharp and pointed as betweens, therefore they don't go through the layers of the quilt so easy.