I am already aware of the notation differences. But is it the only criterion?
Based on written/published records.
First written record from Newton: De analysi per aequationes numero terminorum infinitas (written: 1669; published: 1711).
First published record from Newton: Tractatus de Quadratura Curvarum (1704).
First published paper from Leibniz: Nova Methodus pro Maximis et Minimis (1684).