Mechanism with a small activation energy or one with large activation energy

Rate depends on the rate constant. The rate constant depends on temperature and activation energy. If you have lower activation energy the rate will be higher. This is why catalysts are added since catalysts provide an alternate pathway that requires lower activation energy and catalysts are added to increase the rate of reaction.

Explanation:

This is only the answer if you were asking:

"Which corresponds to the faster rate: a mechanism with a small activation energy or one with a large activation energy?"

Thats what I understood about your question.