As far as ease goes, Delts. As far as painlessness goes, Glutes. Quad are hit and miss for me. Sometimes they are painless, and sometimes I hit a nerve or come close and ache for DAYS. Calves are weird shots, they are easy, kinda painful, but not too painful. I shot one bi once, with **'s Prop/Susp, and my arm turned red for about a week!