Is MS Excel a better database OR MS Access and which among the two is more secured?

MS Access

Excel is not a database it is a tools to keep data with limited functions but access is a database application you can use it.
if you are looking for secure database you have to use Oracle if you ask for application help you in your work as a document controller use SharePoint

MS Access is more secured but MS excel is more easy to use and we can export / import data from both database.

MS Excel is not considered a database per se but even if we include it as a database, MS Access is better becasue Access has an integrated Database Management System (DBMS) that allows us to define, create, query, update, and administer our databases. There is no such functionality in Excel that is more like a Data Analysis Application than a Database System.