Totally depends on the snake. Some will eat with it just laying there. Some you have to make the rat dance a bit. Some just wont eat a F/T.
For me F/T is better cause finding feeding rats in my area is not easy. I have found a couple people who sell rats (when they have some available) but sometimes its very hard to find a live rat that is the proper size for my different sized BPs. I am trying to switch all mine to F/T so I always know I have food for them and proper sized food at that.