Which requirements management system is the easiest to learn and functional?

Question

Software and Internet Services

I was given the task of compiling a TOR and technical requirements for the backend for the project, the head of the direction himself is busy all day, fighting with customers and competitors, as a result, it turns out that the tasks are divided between the department employees.
Please help me, how to make the requirements for the same backend?
Practice shows that you need to use software
Currently, such requirements management systems as IBM Rational RequisitePro, Telelogic DOORS, Sybase PowerDesigner and Borland Caliber RM are widely used.
And what and how to work with it is not clear to me yet ...
Although I understand that these systems are convenient in that synchronization between developers is immediate
. Here, which is better?
JIRA vs Rational Team Concert vs Redmine vs Trello