Most of the cell libraries provide a dedicated inverters and buffers set for CTS. They're specific for this use since they provide balanced rise/fall transitions, typically named as CKINV*/CKBUF* in the libraries. I myself prefer CKINV* instead of CKBUF* aiming for lower CT power. In most of the CKBUF*s I have seen in libraries have quite larger transistors in the second stage (of 2 cascaded inverters) which is over killing for CT timing and area. It all depends on the properties of the cells in your .lib. You need to do an experiment to see what suits your need.What happens if we use only inverters in the clock path instead of buffers?