CIR When setting up T1 and Frame relay

I am in the process of setting up a T1 line to the internet and Setting up frame relay to other location. The three Providers i am trying to get quotes on are as Follows sprint,At&t and World com. at@t and world com are using CIR of 64k and sprint has none. It was exsplined to me that if you use 64k CIR’s you will only use a steping tool to get the 128k and stay at the speed for only a few seconds and the the CIR will start steping you down is this true or is it just a salesmen pitch. Is a cir of 0 Better than a cir of 64K.