Cat harnesses are best for taking a cat on a leash

Two styles of Fur Pets Only cat harnesses are shown here
The light blue is a figure eight (8)  The advantage of a figure "8" cat harness is that the cat cannot escape from it if it is properly adjusted. 

The Pink one is a figure "H" which has the advantage of being easy to put on and remove.

These harnesses are better for use with a cat than small dog harnesses.  The figure eight is ideal for training a cat to walk on a leash because, once adjusted to fit a cat cannot get out of this style harness.  

The figure "H" is better suited for the  cat that has already learned to walk on a leash.