The prior poster is right. If you have to cull, a sharp pair of scissors to cut the head off is quickest and likely most humane for the chick, though often tough for the humans to stomach!
That said, the prior poster is also correct that you RARELY, if ever, have to cull a chick just for bent toes. A young chick's toes are soft and quite pliable, and are easily splinted straight. Just take a piece of cardboard and some duct tape, and tape the chick's foot to it so that the toes are straight. It will fall off eventually. Check the toes then, and re-splint if necessary.