I dont believe that makes difference. What does ruin your battery faster is constantly leaving it on the charger or charging it when the batteries half full all the time. Your supposed to let your phone battery almost die before you charge it, which isnt always convienent, but it wears your battery down faster and makes your phone not stay charged as long.
I always used to charge my phone while it was on, until I was told that my battery gets damaged everytime I charge it when its on. It doesnt make a difference to me, my phone still dies quick, and I've only had this phone since July this year.