Doubt in Perfomance in SQL

A question that has arisen now, and which I always see in one form or another in procedure SQL, is as follows: NOT TABELA.CAMPO IS NULL or TABELA.CAMPO IS NOT NULL . What's the difference in practice in performance issues, run time, from one to the other? Would the perfomance be affected, depending on the number of records in the table and / or the existence of the index in the field?